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A SYSTEM OF MIDWIFERY.
by
EDWARD RIGBY, M. D.,
Physician To the General Lying-In Hospital, Lecturer on Midwifery, at St. Bartholomew's Hospital, etc. etc.
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A SYSTEM OF MIDWIFERY.
With Numerous Wood Cuts.
by
EDWARD RIGBY, M. D.,
Physician to the General Lying-In Hospital, Lecturer on Midwifery, at St. Bartholomew's Hospital, etc. etc.
With Notes and Additional Illustrations.
Philadelphia: Lea & Blanchard. 1841.
Entered, according to the Act of Congress, in the year 1841, by Lea & Blanchard, in the District Court for the Eastern District of Pennsylvania.
Griggs & Co., Printers.
THE EDITOR'S PREFACE.
This System of Midwifery, complete in itself, was published in London, as a part of Dr. Tweedie's "Library of Medicine." The first series of the Library, that on "Practical Medicine," recently completed, has been received with extraordinary favour on both sides of the Atlantic, and the character of the publication is fully sustained in the present contribution by Dr. Rigby, and will secure for it additional patronage.
The late Professor Dewees, into whose hands this volume was placed, a few weeks before his death, in returning it, expressed the most favourable opinion of its merits; and the judgment of such high authority renders it supererogatory to add a word farther of commendation.
It is only necessary for the editor to say that the production of the author is so complete as to have rendered his labour a light one. He has restricted himself mainly to such additions and references as he conceived would render the work more useful to American practitioners. The object of the publication being to present the most condensed view of each subject, he believed it to be inexpedient to depart from the plan by making extensive additions, and entering into the discussion of controversial points, most of which are of minor practical importance.
I. THE PELVIS
Ossa innominata.--Sacrum.--Coccyx.--Distinction between the male and female pelvis.--Diameters of the pelvis.--Pelvis before puberty.--Axes.--Inclination, 15
II. FEMALE ORGANS OF GENERATION
Internal and external.--Ovaria.--Ovum.--Corpus luteum.-- Fallopian tubes.--Uterus.--Vagina.--Hymen.--Clitoris.-- Nymphæ.--Labia, 22
III. DEVELOPMENT OF THE OVUM
Membrana decidua.--Chorion.--Amnion.--Placenta.--Umbilical cord.--Embryo.--Foetal circulation, 48
I. SIGNS OF PREGNANCY
Difficulty and importance of the subject.--Diagnosis in the early months.--Auscultation.--Changes in the vascular and nervous systems.--Morning sickness.--Changes in the appearance of the skin.--Cessation of the menses.--Areola.--Sensation of the child's movements.--"Quickening."--Auscultation.--Uterine souffle.--Sound of the foetal heart.--Funic souffle.--Sound produced by the movements of the foetus.--Ballottement.--State of the urine.--Violet appearance of the mucous membrane of the vagina.--Cases of doubtful pregnancy.--Diagnosis of twin pregnancy, 80
II. TREATMENT OF PREGNANCY
Sympathetic affections of the stomach during pregnancy.-- Morning sickness.--Constipation.--Flatulence.--Colicky pains.--Headach.--Spasmodic cough.--Palpitation.--Toothach.-- Diarrhoea.--Pruritus pupendi.--Salivation, 101
III. SIGNS OF THE DEATH OF THE FOETUS
Difficulty of the subject.--Signs before labour.--Motion of the foetus.--Sound of the foetal heart.--Uterine souffle.-- Signs during labour where the head presents--where the face, the nates, the arm, or the cord, present.--Fetid liquor amnii.--Discharge of meconium, 107
IV. MOLE PREGNANCY
Nature and origin.--Varieties.--Diagnostic symptoms.-- Treatment, 112
V. EXTRA-UTERINE PREGNANCY
Tubarian, ovarian, and ventral pregnancy.--Pregnancy in the substance of the uterus, 117
VI. RETROVERSION OF THE UTERUS
History.--Causes.--Symptoms.--Diagnosis.--Treatment.-- Spontaneous terminations, 126
VIII. PREMATURE EXPULSION OF THE FOETUS
Abortion.--Miscarriage.--Premature labour.--Causes.-- Symptoms.--Prophylactic measures.--Effects of repeated abortion.--Treatment, 141
I. STAGES OF LABOUR
Preparatory stage.--Precursory symptoms.--First contractions.--Action of the pains.--Auscultation during the pains.--Effect of the pains upon the pulse.--Symptoms to be observed during and between the pains.--Character of a true pain.--Formation of the bag of liquor amnii.--Rigour at the end of the first stage.--Show.--Duration of the first stage.-- Description of the second stage.--Straining pains.--Dilatation of the perineum.--Expulsion of the child.--Third stage.-- Expulsion of the placenta.--Twins, 156
II. TREATMENT OF NATURAL LABOUR
State of the bowels.--Form and size of the uterus.--True and spurious pains.--Treatment of spurious pains.--Management of the first stage.--Examination.--Position of the patient during labour.--Prognosis as to the duration of labour.--Diet during labour.--Supporting the perineum.--Treatment of perineal laceration.--Cord round the child's neck.--Birth of the child, and ligature of the cord.--Importance of ascertaining that the uterus is contracted after labour.--Management of the placenta.--Twins.--Treatment after labour.--Lactation.--Milk fever and abscess.--Excoriated nipples.--Diet during lactation.--Management of lochia.--After-pains, 169
III. MECHANISM OF PARTURITION
Cranial presentations--first and second position.--Face presentations--first and second positions.--Nates presentations, 199
I. THE FORCEPS
Description of the straight and curved forceps.--Mode of action.--Indications.--Rules for applying the forceps.-- History of the forceps, 216
II. TURNING
Turning.--Indications.--Circumstances most favourable for this operation.--Rules for finding the feet.--Extraction with the feet foremost.--Turning with the nates foremost.--Turning with the head foremost.--History of turning, 230
III. CÆSAREAN OPERATION
Indications,--Different modes of performing the operation.-- History of the Cæsarean operation, 243
IV. ARTIFICIAL PREMATURE LABOUR
History of the operation.--Period of pregnancy most favourable for performing it.--Description of the operation, 250
V. PERFORATION
Variety of perforators.--Indications.--Mode of operating.-- Extraction.--Crotchet.--Embryulcia, 256
I. FIRST SPECIES OF DYSTOCIA
Malposition of the child.--Arm or shoulder the only faulty position of a full-grown living foetus.--Causes of malposition.--Diagnosis before and during labour.--Results where no assistance is rendered.--Spontaneous expulsion.-- Malposition complicated with deformed pelvis or spasmodically contracted uterus.--Embryulcia.--The prolapsed arm not to be put back or amputated.--Presentation of the arm and head.-- Presentation of the hand and feet.--Presentation of the head and feet.--Rupture of the uterus.--Usual seat of laceration.-- Causes.--Premonitory symptoms.--Symptoms.--Treatment.-- Gastrotomy.--Rupture in the early months of pregnancy, 264
II. SECOND SPECIES OF DYSTOCIA
Size and form of the child.--Hydrocephalus.--Cerebral tumours.--Accumulation of fluid and tumours in the chest or abdomen.--Monsters.--Anchylosis of the joints of the foetus, 281
III. THIRD SPECIES OF DYSTOCIA
Difficult labour from faulty condition of the parts which belong to the child.--The membranes.--Premature rupture of the membranes.--Liquor amnii.--Umbilical cord.--Knots upon the cord.--Placenta, 286
IV. FOURTH SPECIES OF DYSTOCIA
Abnormal state of the pelvis.--Equally contracted pelvis.-- Unequally contracted pelvis.--Rickets.--Malacosteon, or mollities ossium.--Symptoms of deformed pelvis.--Funnel-shaped pelvis.--Obliquely distorted pelvis.--Exostosis.--Diagnosis of contracted pelvis.--Effects of difficult labour from deformed pelvis.--Fracture of the parietal bone.--Treatment.--Prognosis, 292
V. FIFTH SPECIES OF DYSTOCIA
Obstructed Labour from a Faulty Condition of the Soft Passages.
Pendulous abdomen.--Rigidity of the os uteri.--Belladonna.-- Edges of the os uteri adherent.--Cicatrices and callosities.-- Agglutination of the os uteri.--Contracted vagina.--Rigidity from age.--Cicatrices in the vagina.--Hymen.--Fibrous bands.-- Perineum.--Varicose and oedematous swellings of the labia and nymphæ.--Tumours.--Distended or prolapsed bladder.--Stone in the bladder, 308
VI. SIXTH SPECIES OF DYSTOCIA
Faulty Labour from a Faulty Condition of the expelling Powers.
I. Where the uterine activity is at fault--functionally or mechanically--from debility--derangement of the digestive organs--mental affections--the age and temperament of the patient--plethora--rheumatism of the uterus--inflammation of the uterus--stricture of the uterus.--Treatment. II. Where the action of the abdominal and other muscles is at fault.--Faulty state of the expelling powers after the birth of the child.-- Hæmorrhage.--Treatment, 324
VII. INVERSION OF THE UTERUS
Partial and complete.--Causes.--Diagnosis and symptoms.-- Treatment.--Chronic inversion.--Extirpation of the uterus, 345
VIII. ENCYSTED PLACENTA
Situation in the uterus.--Adherent placenta.--Prognosis and treatment.--Placenta left in the uterus.--Absorption of retained placenta, 354
IX. PRECIPITATE LABOUR
Violent uterine action.--Causes.--Deficient resistance.-- Effects of precipitate labour.--Rupture of the cord.-- Treatment.--Connexion of precipitate labour with mania, 361
X. PROLAPSUS OF THE UMBILICAL CORD
Diagnosis.--Causes.--Treatment.--Reposition of the cord, 368
XI. PUERPERAL CONVULSIONS
Epileptic convulsions with cerebral congestion.--Causes.-- Symptoms.--Tetanic species.--Diagnosis of labour during convulsions.--Prophylactic treatment.--Treatment--Bleeding.-- Purgatives.--Apoplectic species.--Anæmic convulsions.-- Symptoms.--Treatment.--Hysterical convulsions.--Symptoms, 376
XII. PLACENTAL PRESENTATION, OR PLACENTA PRÆVIA
History.--Dr. Rigby's division of hæmorrhages before labour into accidental and unavoidable.--Causes.--Symptoms.-- Treatment.--Plug.--Turning.--Partial presentation of the placenta.--Treatment, 393
XIII. PUERPERAL FEVERS
Nature and varieties of puerperal fever.--Vitiation of the blood.--Different species of puerperal fever.--Puerperal peritonitis.--Symptoms.--Appearances after death.-- Treatment.--Uterine phlebitis.--Symptoms.--Appearances after death.--Treatment.--Indications.--False peritonitis.-- Treatment.--Gastro-bilious puerperal fevers.--Symptoms.-- Appearances after death.--Treatment.--Contagious or adynamic puerperal fevers.--Symptoms.--Appearances after death.-- Treatment, 415
XIV. PHLEGMATIA DOLENS
Nature of the disease.--Definition of phlegmatia dolens.-- Symptoms.--Duration of the disease.--Connexion with crural phlebitis.--Causes.--Connexion between the phlegmatia dolens of lying-in women and puerperal fever.--Anatomical characters.--Treatment.--Phlegmatia dolens in the unimpregnated state, 463
XV. PUERPERAL MANIA
Inflammatory or phrenitic form.--Treatment.--Gastro-enteric form.--Treatment.--Adynamic form.--Causes and symptoms.-- Treatment, 473
INDEX, 483
A SYSTEM OF MIDWIFERY.
Introduction
By the term Midwifery is understood the knowledge and art of treating a woman and her child during her pregnancy, labour, and the puerperal state. We employ it in this extended sense, because most systematic writers of later times have adopted this arrangement. The terms, Art des Accouchemens of the French, the Ostetricia, and Arte della Parteria, of the Italians and Spaniards, and the Geburtshülfe of the Germans, are restricted to the process of parturition, although they have been and continue to be, used in the same extended sense as that in which we propose to use the term Midwifery.
Although pregnancy and parturition, strictly speaking, are perfectly natural functions, yet they involve such a complication and variety of other processes, and also changes of such extent, that the whole system is rendered more or less subservient to them during the periods of their existence: hence, therefore, their number and variety must ever render them more or less liable to deviations and irregularities of action, which will necessarily be aggravated by the effects of civilized life, and in many instances are productive of derangement in the general economy of the system. Under such circumstances the irritability of the system increases at the expense of its strength and vigour, and not only increases its liability to these derangements, but diminishes its power of resisting their effects.
In order that we may render the nature and treatment of the changes and phenomena, which take place in the human system during the periods above alluded to, more intelligible, we shall take a short anatomico-physiological view of the structure, form, arrangement, and function of the parts and organs which are more or less directly concerned in these important processes. This will embrace the subject of embryology, a department of physiological knowledge, which, though it has lately been much enriched by valuable discoveries, still affords a rich field of investigation and research.
The diagnosis and course of healthy pregnancy, and its various diseases, terminating with the subject of healthy parturition and its treatment will form the subject of the succeeding part.
Parturition properly speaking, will come under two separate heads eutocia and dystocia; the one signifying natural or favourable labour, the other, unnatural, faulty, or unfavourable labour.
The concluding part will contain a short account of some of the more important diseases which occur to the female during the first month after parturition.
I. THE PELVIS
Ossa innominata.--Sacrum.--Coccyx.--Distinction between the male and female pelvis.--Diameters of the pelvis.--Pelvis before puberty.-- Axes.--Inclination.
The Pelvis, as the frame-work which, in great measure, contains, supports, and protects, the complicated apparatus of the generative organs, first claims our attention; since an accurate knowledge of the form, size, and uses, of its different parts is indispensably necessary, not only to understand the situation of the viscera it contains, but also to form a correct view of the mechanism upon which the process of parturition depends.
This osseous canal or circular archway, consists essentially of three bones, the right and left os innominatum, which form the sides of the arch, with the sacrum between them, acting as a keystone, and supporting the whole weight of the trunk above.
Ossa innominata. The ossa innominata in early life consists of three distinct bones, the iliac or hip bones at the sides, the ischia or lower portion upon which we sit, and the ossa pubis which meet each other anteriorly to form the front part of the pelvis. In the adult these are consolidated into one bone, merely leaving irregular lines and ridges here and there to mark their previous existence.
These bones present several striking points of resemblance with those which belong to the upper extremities, viz. the scapula and clavicle; and in the early stages of development, this similarity is much more distinctly seen: it is remarkable, that although the ischia and ossa pubis are formed later than the ilia, yet they unite with each other much sooner than with the ilia, so that the two consolidated bones bear the same relation to the ilium which is separated from them, that the clavicle does to the scapula: many other points of resemblance between the bones of the shoulder and pelvis might be noticed if necessary. (Meckel, Anat. vol. ii. p. 239.) The ossa innominata meet each other in front, forming the symphysis pubis, having layers of fibro-cartilage interposed between their extremities, and bound together by ligamentous fibres constituting the ligamentum arcuatum, or annulare ossium pubis, and by which a more rounded appearance is given to the pubic arch. They are united to the sacrum posteriorly, one on each side of it, forming the right and left sacro-iliac symphysis or synchondrosis; this differs in many respects from the symphysis pubis, the cartilaginous coverings of the opposing bones being much thinner, especially those of the ossa innominata; the surfaces are extremely uneven from the deep indentations which each bone presents at this part, locking, as it were, into each other, and thus contributing greatly to increase the firmness of the joint, which is also still farther strengthened by the support of powerful ligaments.
Between the ligamento-and cartilaginous layers which cover the surfaces of the bones at the pubic and sacro-iliac symphyses, a minute collection of synovial fluid may be detected, like that found in the fibro-cartilages between the vertebræ; it serves to lubricate their surfaces, and separates them more or less, thereby increasing the thickness of the intervening cartilaginous structure; and separating also the edges of the bones, to a certain extent, more especially at the symphysis pubis. (Portal, Anat. Méd.) These laminæ of intervening fibro-cartilage are thicker in the female than in the male, although of smaller extent; and this is still more remarkable during pregnancy, this ligamento-cartilaginous structure becoming now more cushiony and elastic, while in the latter months we can easily distinguish blood-vessels ramifying through it, which are branches of the pudic arteries and veins.
Sacrum. The sacrum, which forms the upper and posterior portion of the pelvis, contributes greatly to the general solidity of the whole bony circle. From its wedge-like shape, it is admirably adapted to support the entire weight of the trunk, and acts, as we have before observed, as a kind of keystone to the arch which is formed by the ossa innominata. It is of a triangular shape, being concave before and convex behind. In the foetus it consists of five distinct pieces of bone separated by intervening layers of cartilage, like the vertebræ of the spinal column, and from their resemblance to those bones they have been called false vertebræ. These cartilages, after a time, gradually disappear; bony matter is deposited in their place; so that by the period of puberty the five sacral vertebræ become united into one solid bone, although they may be distinguished, until an advanced period of life, by the ridges which their edges form.
The upper surface of the sacrum, having to sustain the whole weight of the spinal column, is broad and flat, and corresponds to the lower surface of the last lumbar vertebra. Its anterior surface forms with that of the other mentioned bone a considerable angle, which projects forwards and more or less downwards towards the symphysis pubis, and is called the promontory of the sacrum. Beneath this point, the sacrum takes a considerable sweep backwards as it descends, gradually advancing again forwards, as we approach its inferior extremity, forming an extensive concavity upon its anterior surface: this is termed the hollow of the sacrum.
Coccyx. The lower end is prolonged by a small bone, called Coccyx or os Coccygis, from its supposed resemblance to a cuckoo's beak. It usually consists of four, and sometimes (especially in women) of five portions; they are much smaller than the bones of the sacrum, and are very imperfect rudiments of vertebral formation; like these, they are at an early period little else than cartilage, and even when the bones are fully formed, they are united by intermediate cartilage, and thus retain so much mobility upon each other, as well as upon the lower end of the sacrum, as to admit of being forced backwards to the extent of a full inch, thus contributing greatly to increase the capacity of the outlet.
The sacrum not only serves to form the posterior parietes of the pelvis, but by the curve which its lower portion takes forwards, together with the coccyx, it gives a powerful support to the pelvic viscera.
When we take a general view of the bones which collectively form the pelvis, we find that it is evidently divided into two portions--an upper and a lower one. On the Continent these have been called the large and the small pelvis; in Britain we merely speak of the pelvis above or below the brim, the line of demarcation being the linea ilio-pectinea at the sides, the crista of the os pubis in front, and the promontory of the sacrum behind. The alæ of the ilia form a prominent feature in the upper pelvis, and not only afford an attachment for numerous muscles, but furnish a powerful and ample means of protection and support to the pelvic and lower abdominal viscera. In the female pelvis this is remarkably the case, the cavitas iliaca being well expanded and of greater extent than in the male, the crista of the ilium thrown more outwards; hence the distance between the antero-superior processes is much more considerable.
Distinction between the male and female pelvis. At the brim, the female pelvis presents several well-marked points of distinction from that of the male. The male pelvis has a contracted brim of a rounded or rather triangular form, with the promontory of the sacrum considerably projecting; whereas, that of the female is spacious, of an oval shape, and with a slightly prominent sacrum, thus affording more room for the passage of the child through the brim. The cavity of the male pelvis is deep, while in the female pelvis it is shallow, a circumstance which is very strikingly seen in comparing the length of the symphysis pubis in each, that of the male pelvis being nearly double the length of the female. This is an important point of difference as regards parturition, because in a shallow pelvis, the extent of surface exposed to the pressure of the head will be much less than where it is deep, and hence the resistance to the passage of the child will be proportionably diminished: in confirmation of this, we find that tall women, in whom the pelvis is usually deep, do not, on the whole, bear children so easily as women of middling stature in whom the pelvis is more shallow. The capacious hollow of the sacrum in the female pelvis adds also greatly to the extent of its cavity, and peculiarly adapts it for parturition, the injurious pressure of the head upon the soft linings of the pelvis being thus prevented, and every facility afforded for its quick and easy transit through the cavity. This applies especially to the neck of the bladder, which would almost inevitably suffer in every labour, were it not for the ample hollow of the sacrum relieving the pressure of the head against the anterior portions of the pelvis. The bones of the female pelvis being more slender and delicately formed, the foramina ovalia and sacro-ischiatic notches are wider, and thus add still farther to the capacity of the cavity.
In no part of the pelvis is the difference between the sexes more strongly marked than at the outlet. The spacious and well-rounded arch of the pubes in the female of the slender rami, is a striking contrast to the contracted angular arch of the male pelvis; and the tuberosities of the ischium being much wider apart, the head is enabled to pass under the arch with greater facility, and thus still farther to relieve the anterior of the pelvis from its pressure. The length of the sacro-sciatic ligaments, and the mobility of the coccyx upon the sacrum, by which it can be forced backwards to the extent of an inch by the pressure of the head during labour, not merely serve to distinguish it from the male pelvis, but afford a beautiful instance of design and adaptation.
The greater width of the pubic arch in the female pelvis is seen by comparing its angle with that of the arch in the male pelvis. In the female it has been estimated to form an angle varying between 90° and 100°, whereas in the male it is not more than between 70° and 80°. (Osiander, Handbuch der Embindungs-kunst, cap. iv. p. 58.)
From the greater width of the female pelvis, the acetubula are farther apart, and the great trochanters of the thigh-bones more projecting; hence the greater motion of the hips in the female when she walks, which is still more visible when she runs, for the motion is communicated to the whole trunk, so that each shoulder is turned more or less forwards as the corresponding foot is advanced. The thigh-bones, which are so far apart at their upper extremities, approach each other at the knees, contributing to produce that unsteady gait which is peculiar to the sex. "The woman," says Mr. John Bell, "even of the most beautiful form, walks with a delicacy and feebleness which we come to acknowledge as a beauty in the weaker sex." (Bell's Anat. vol. i.)
These characteristic marks of the female figure, upon which its beauty in great measure depends, are well seen in all great works of art, whether of sculpture or painting. "The ancients," as Mr. Abernethy has observed, "who had a clear and strong perception of whatever is beautiful or useful in the human figure, and who, perhaps, delicately exaggerated beauty to render it more striking, have represented Venus as measuring one-third more across the hips than the shoulders, whilst, in Apollo, they have reversed these measurements." (Physiological Lectures.)
Diameters of the pelvis. It is of the utmost importance to the obstetrician, that he should be thoroughly acquainted with the various dimensions of the female pelvis, for, without this, he can form no correct idea of the manner in which the presenting part of the child passes through its brim, cavity and outlet during labour; indeed, unless he be thoroughly versed in this necessary point of obstetric knowledge, he will remain in almost total ignorance of the whole mechanism of parturition, which must, in great measure, be looked upon as the basis of practical midwifery. The dimensions of the brim cavity and outlet of the pelvis may be given with sufficient correctness for all practical purposes, by measuring three of their diameters,--1. the straight, antero-posterior, or conjugate; 2. the transverse; and 3. the oblique. At the brim they are as follow:--the straight diameter, drawn from the middle of the promontorium sacri to the upper edge of the symphisis pubis, 4·3 inches; the transverse diameter, from the middle of the linea-ilio-pectinea of one ilium to that of the other, 5·4 inches; and the oblique diameter, from one sacro-iliac synchondrosis to the opposite acetabulum, 4·8 inches. The oblique diameters are called right and left, according to the sacro-iliac symphysis from which they are drawn.
In the cavity these dimensions vary more or less. The straight diameter, measured from the centre of the hollow of the sacrum to that of the symphysis pubis, is 4·8 inches; the transverse, from the point corresponding to the lower margin of the acetabulum on one side to that of the other, 4·3; and the oblique, drawn from the centre of the free space formed by the sacro-ischiatic notch and ligaments on one side of the foramen ovale of the other, 5·2.
At the inferior aperture or outlet the alteration is still more remarkable. The straight diameter, from the point of the coccyx to the lower edge of the symphysis pubis, measures only 3·8 inches; but from the mobility of the coccyx enabling it to be pushed back during labour to the extent of a whole inch, it is capable of being extended to 4·8 inches. The transverse diameter from one tuberosity of the ischium to the other, measures 4·3 inches: and the oblique, from the middle of the lower edge of the sacro-sciatic ligament of one side, to the point of union between the ischium and descending ramus of the pubes on the other 4·8 inches.
Although these are the proportions of the brim cavity and outlet of the female pelvis in the skeleton state, their real dimensions during life, when the pelvis is thickly lined with muscular and other structures, are very different. The large masses of the psoas magnus and iliacus internus, besides other muscles of inferior size, contribute to alter materially the relations of the pelvic diameters to each other; hence we find that, so far from being the longest, the transverse diameter is one of the shortest, being little more than the antero-posterior. This holds good, especially during labour, because these muscles being thrown into powerful contraction, their bellies swell, and thus tend still farther to diminish its length. The oblique diameters are, in fact, the longest during life, because not only are the parietes of the pelvis at the brim covered by a very thin layer of soft tissues in these directions; but as the extremities of these diameters, in the cavity and outlet, correspond to free spaces which are merely filled up with soft yielding structure, it follows that their length can be somewhat increased when pressure is applied in these directions; the antero-posterior diameter of the outlet can alone be compared with the oblique diameters in this respect, and then only when the coccyx is forced backwards to its full extent by the pressure of the head.
Pelvis before puberty. The proportions of the adult female pelvis are no longer what they were during childhood; before the age of puberty they resemble those of the male pelvis, the brim being contracted and more or less triangular, and the antero-posterior diameter equalling or even exceeding the transverse. Indeed, at a still earlier period, it presents many points of resemblance even to the pelvis of animals; as, however, growth and development advance, and the various changes which constitute puberty take place, the transverse diameters of the brim, cavity, and outlet increase at the expense of the antero-posterior, until at length, it has assumed the proper proportions of the adult female pelvis.
Axes. Of not less importance is it that the obstetrician should be thoroughly acquainted with the direction which the central line or axis of the entrance and outlet of the pelvis takes. The axis of the superior aperture has been considered to form with the horizon an angle varying between 50° and 60°; this was noticed long ago by Dr. Smellie: "when the body of a woman," says this valuable author, "is reclined backwards, or half sitting half lying, the brim of the pelvis is horizontal; and an imaginary straight line, descending from the navel, would pass through the middle of the cavity; but in the last month of pregnancy such a line must take its rise from the middle space between the navel and scrobiculus cordis in order to pass through the same point of the pelvis." (Treatise of Midwifery, book i. chap. i. sect. 2.)
Inclination of the pelvis. The angle which the axis of the superior aperture of the pelvis forms with the horizon, when a woman is in the upright posture, necessarily marks what has been called the inclination of her pelvis, and varies, of course, in proportion to the angle which the above mentioned axis forms. In a tall woman of slender figure, where the different curves of the spinal columns are slight, the inclination of the pelvis is much less than in a short thick set woman, where the spine is much more strongly curved. Where the inclination is slight, the hollow of the sacrum is generally small, and the vulva directed more forwards; where, on the other hand, the pelvis is much inclined, the hollow of the sacrum is generally observed to be deep, and the vulva directed more or less backwards. The axis of the lower aperture or outlet appears to depend, in great measure, on the curve which the lower part of the sacrum takes downwards and forwards; but, as a general rule, we think it will be found to form, more or less, a right angle with the axis of the brim. The greater the angle which the axis of the brim forms with the horizon, the less will be that which the axis of the outlet forms, and vice versâ; or, in other words, the angle with the horizon which the axis of the one forms is inversely to that of the other.
The consideration of the various deviations, as to size and form, from the natural proportions which the female pelvis occasionally presents, belongs, more strictly speaking, to that species of faulty labour which arises from these conditions. We, therefore, refer to the fourth species of dystocia, viz. Dystocia Pelvica, where the different pelvic anormalities are described.
II. FEMALE ORGANS OF GENERATION
Internal and external.--Ovaria.--Ovum.--Corpus luteum.--Fallopian tubes.--Uterus.--Vagina.--Hymen.--Clitoris.--Nymphæ.--Labia.
The female organs of generation have been usually classed by the English authors under the two heads of internal and external; a similar arrangement has also been followed by the Continental writers, but with the advantage of using distinctive terms which are more expressive of their peculiar functions, viz. the formative and copulative organs. Under the first are included the ovaria, Fallopian tubes, and uterus: under the second, the vagina and external parts. We propose to give a short description of these in the unimpregnated state, and then to describe the changes which they present during pregnancy, labour, and the puerperal condition. In point of situation and arrangement they bear a considerable resemblance to the generative organs in the male, being situated at the lower portion of the trunk, and arranged in symmetrical order, so that they either occur in pairs, one on each side the median line of the body, or singly, being equally divided by it throughout their whole length. Although there is in many points considerable difference between the male and female organs, still there is sufficient resemblance to entitle them to be considered as being formed upon the same fundamental type, a resemblance which is seen still more strikingly in the early periods of foetal life. They differ essentially from all the other organs of the system, being in activity during a portion of a woman's life only, and then only at intervals.
Ovaria. The ovaries are situated in the upper part of the cavity of the pelvis, one on each side, near to the uterus, to which they are merely attached by a ligament (the ligamentum ovarii) which is a portion of that duplicature of the peritoneum which connects the uterus to the pelvis, and is known by the name of ligamentum latum, or broad ligament.
They are of an oval figure; their anterior and posterior surface is convex, the superior margin is also convex, while their lower edge is straight or somewhat concave: towards their inner and outer extremities they become thinner.
Their external surface in the virgin state is usually smooth, but in advanced age they become uneven and shrivelled; when fully developed they are about an inch and a half in length: their greatest breadth, which is at that portion of the ovary which is farthest from the uterus, is half an inch; their thickness is somewhat less.
The ovaries are supplied with blood by the spermatic arteries, which are of course considerably shorter in the female; they pass between the two layers of the broad ligament to the ovarium, assuming there a beautifully convoluted arrangement, very similar to the convoluted arteries of the testis. These vessels traverse the ovary nearly in parallel lines, forming numerous minute twigs, which have an irregular knotty appearance from their tortuous condition, and appear to be chiefly distributed to the Graafian vesicles. The external covering of the ovaries is formed by peritoneum, which here receives the name of Inducium; it envelopes the parenchymatous tissue of the gland called stroma, which is a dense laminar cellular tissue of a reddish colour; its external portion which is in contact with and firmly adherent to the indusium, is condensed into a species of covering of a firm structure and whitish colour, and is called the tunica albuginea of the ovary. In the substance of the stroma are embedded a number of vesicles of various sizes, which, although previously described by Vesalius and Fallopius, have been called Graafian vesicles, after De Graaf. These do not commonly become visible until the seventh year, from which period they gradually enlarge until puberty, when the ovaries increase in size, become softer and more vascular, and one or two of these vesicles may be observed to be larger, more developed, and projecting considerably from the surface of the gland.
The proper capsule of the Graafian vesicle is composed of two layers. The outer is formed of dense cellular tissue, in which are ramified many blood vessels; the inner layer is thicker, softer, and more opaque than the preceding, to which it is closely united, and from which it receives vascular twigs.
Ovum. The contained part or nucleus of the vesicle of De Graaf consists of, first, a granulary membrane, enclosing, secondly, a coagulable granular fluid; thirdly, connected with the granulary membrane on one side is a circular mass or disc of granulary matter, in the centre of which is embedded, fourthly, the ovum.
This disc, called by Baer the proligerous disc, presents in its centre on the side towards the interior of the vesicle, a small rounded prominence, called the cumulus, and on the opposite side a small cup-like cavity hollowed out in the cumulus. The cavity is for the reception of the ovum.[1]
From the very minute size of the human ovum, and the difficulty of detecting it, the existence of this little corpuscule was not satisfactorily ascertained until modern times. Although De Graaf had observed ova in the Fallopian tube so early as 1668, which fact had been confirmed by the researches of Dr. Haighton and Mr. Cruickshank, still, as no traces of such ova had been discovered in the Graafian vesicle, and as it was evident that the Graafian vesicle, from its size, &c. could not pass along the Fallopian tube, it was concluded that the inner surface of the vesicle was a species of glandular structure which secreted the fluid with which it was filled, and which was analogous to the semen of the male testicle; hence, in former times, the ovaries were known by the name of testes muliebres. The celebrated anatomist Steno[2] first pointed out the analogy between these organs and the ovaries of the fish tribe: this view was afterwards supported by De Graaf,[3] and they have since continued to retain the name of ovaries.
To Professor von Baer, now of St. Petersburg, is due the merit of having first pointed out the distance of the ovum in the Graafian vesicle, and of thus putting beyond all doubt the accuracy of De Graaf's observations, as well as those of Dr. Haighton and Mr. Cruickshank.
Corpus luteum. Upon impregnation taking place, one or more of the most prominent Graafian vesicles begins to show marks of considerable vascularity, both in its external capsule and in the surrounding stroma of the ovary. The vesicle swells, and at length bursts, discharging its contents into the funnel-shaped extremity of the Fallopian tube, which firmly grasps the ovary at this point by means of its fimbriæ.
These changes begin to take place immediately after impregnation; the inner lining of the vesicle, which Professor von Baer considers to be a mucous membrane, appears to undergo a rapid development, much more so than the external capsule which contains it. It is, therefore, thrown into a number of corrugations by which the cavity of the vesicle is greatly diminished; it becomes much thicker, and assumes a yellow colour. As its growth proceeds, the cavity of the vesicle becomes still farther contracted, until being unable longer to retain its contents, it bursts and discharges them as above described.
The remains of the ruptured vesicle form a round glandular yellow coloured body, called corpus luteum: it projects considerably from the surface of the ovary, attaining the size of a small mulberry. In the middle of this projection there is a little irregular and generally triangular depression or indentation, which is the opening through which the ovum was discharged from the Graafian vesicle: this after a short time closes, forming a little cicatrix on the surface of the ovary.
"Upon slitting the ovarium at this part, the corpus luteum appears a round body, of a very distinct nature from the rest of the ovarium. Sometimes it is oblong or oval, but more generally round. Its centre is white, with some degree of transparency; the rest of its substance has a yellowish cast, is very vascular, tender and friable, like glandular flesh. Its larger vessels cling round its circumference, and these send their smaller branches inwards through its substance: a few of these larger vessels are situated at the cicatrix or indentation on the outer surface of the ovarium, and are there so little covered as to give that part the appearance of being bloody when seen at a little distance."[4] Upon making a section of a corpus luteum, we observe that its cavity has an angular form, from which, as from a centre, white lines radiate to the circumference of the vesicle; an appearance which is evidently produced by the corrugation of the inner membrane of the vesicle, as above alluded to. To a similar cause we may also attribute the lobular appearance, which the structure of the corpus luteum presents when a section is made of it. The number of these corpora lutea corresponds exactly with the number of newly formed ova. Meckel, after having examined no less than two hundred pregnant animals of the class mammalia, found that the number of corpora lutea corresponded exactly with that of the young produced. "When there is only one child," says Dr. W. Hunter, "there is only one corpus luteum, and two in the case of twins. I have had opportunities of examining the ovaria with care in several cases of twins, and always found two corpora lutea. In some of these cases there were two distinct corpora lutea in one ovarium, in others there was a distinct corpus luteum in each ovarium."
A Graafian vesicle cannot be converted into a corpus luteum except by actual and effective sexual intercourse; and the strange and discrepant accounts which have every now and then been published, even by authors of considerable repute, of corpora lutea having been found in the ovaries of virgin and even newly-born animals merely prove that the true characteristics of the corpus luteum were not sufficiently known. The irregular cysts, cavities, or deposites of whitish or yellowish structure which are frequently found in the ovary, independent of impregnation, and which have been improperly enough called virgin corpora lutea, present points of difference so marked that they can scarcely be mistaken by an experienced eye. The angular cavity opening externally, the stellated, radiated, cicatrix-like appearance, which a section of the corpus luteum presents, its soft and delicate structure as described by Dr. Hunter, and above all its vascularity, and the facility with which its vessels can be injected from the general tissue of the ovary, are characters only found in a true corpus luteum. Virgin corpora lutea frequently occur under circumstances of disease, especially those of a tubercular character. They frequently appear as distinct cysts, the walls of which are semi-cartilagenous; at other times they seem to be nothing more than a coagulum of blood: they seldom project much from the ovary, and in no instance have they the peculiar structure of the corpus luteum, nor the external cicatrix, nor are they capable of being injected.
After awhile the cavity of the corpus luteum contracts, and the opening into it closes. The surrounding stroma loses its vascularity, the prominence at this part of the ovary gradually subsides, and the ovary returns to its former size. The periods at which these changes take place vary, but with the exception of those first mentioned they proceed slowly whilst pregnancy lasts, after which time, now that the increased activity of the pelvic circulation peculiar to that period has ceased, they advance more rapidly.
"If an examination be made within the first three or four months after conception, we shall, I believe, always find the cavity still existing, and of such a size as to be capable of containing a grain of wheat at least, and very often of much greater dimensions: this cavity is surrounded by a strong white cyst (the inner coat of the Graafian vesicle,) and as gestation proceeds the opposite parts of this approximate, and at length close together, by which the cavity is completely obliterated, and in its place there remains an irregular white line, whose form is best expressed by calling it radiated or stelliform."[5] Dr. Montgomery adds, "I am unable to state exactly at what period the central cavity disappears, or closes up to form the stellated line. I think I have invariably found it existing up to the end of the fourth month. I have one specimen in which it was closed in the fifth month, and another in which it was open in the sixth: later than this I never found it."
When pregnancy is over, the corpus luteum gradually diminishes and disappears. Dr. Montgomery states that "the exact period of its total disappearance I am unable to state, but I have found it distinctly visible so late as at the end of five months after delivery at the full time, but not beyond this period." Hence it will be seen that in a few months after the termination of pregnancy, all traces of the corpus luteum are lost, and that, therefore, it will be impossible to decide as to how frequently impregnation has taken place, merely by examining the ovaries, as has been supposed. There is also another point to which Dr. Montgomery has alluded, which is well worthy of notice: in mentioning the fact that a vesicle may contain two ova, and thus a woman be delivered of twins, and yet there be but one corpus luteum, he observes that "the presence of a corpus luteum does not prove that a woman has borne a child, although it would be a decided proof that she has been impregnated, and had conceived, because it is quite obvious that the ovum, after its vivification, may be, from a great variety of causes, blighted and destroyed, long before the foetus has acquired any distinct form. It may have been converted into a mole or hydatids: thus, however paradoxical it may at first sight appear, it is nevertheless obviously true, that a woman may conceive and yet not become truly with child, a fact already alluded to, as noticed by Harvey; but the converse will not hold good. I believe no one ever found a foetus in utero without a corpus luteum in the ovary; and that the truth of Haller's carollary, 'nullus unquam conceptus est absque corpore luteo' remains undisputed."
During childhood, the ovaries present a perfectly smooth surface, and their structure appears to be homogeneous, consisting of a dense cellular tissue. About the seventh year, the first traces of the Graafian vesicles make their appearance; as the period of puberty approaches, the whole gland enlarges, becomes softer and more vascular; the Graafian vesicles are more numerous, and generally one or two will be found larger and more prominent than the rest. After repeated impregnations, and especially towards that time of life when the catamenia are about to disappear, the ovary becomes more or less flabby and corrugated, and at a still more advanced age presents a shrivelled appearance.
The ovaries are liable to inflammation and its consequences, more especially abscess, general enlargement, and induration: the malignant changes of structure, viz. cephaloma, hæmatoma, and cancer, rarely have their origin in the ovaries, but extend to these organs from the adjacent parts. Lipomatous or fatty tumours are occasionally met with, containing hair, rudiments of teeth, &c. Cysts not unfrequently occur in the ovaries, and attain a very considerable size; they are simple or compound, sometimes consisting of several cysts one within the other, and distended with fluids, which vary considerably in their character. These tumours come under the general head of OVARIAN DROPSY. The ovaries are also liable to many remarkable morbid changes in the puerperal state, such as softening and complete disorganization, the natural structure of the organ being entirely broken down and converted into a bloody pulpy mass; in some cases the whole gland is apparently dissolved away, so as scarcely to leave a trace of its previous existence.
Fallopian tubes. The Fallopian tubes, which act as excretory ducts to the ovaries, take their course through the upper portion of the broad ligaments, running from without inwards, towards the superior margin of the uterus, the ovaries being situated behind and somewhat above them. They are somewhat contorted, and are considerably more dilated at their abdominal extremity where they are unattached, than where they are connected to the uterus, being as much as from three to four lines at the former point; whereas, at the latter, they are not more than half a line.
Their abdominal extremity, which is like the mouth of a funnel, has its edge strongly fimbriated, and has hence been called the morsus diaboli. Their other extremity opens into the cavity of the uterus at the angle which the fundus forms with its sides, and the whole of the tube is about five inches.
The Fallopian tubes receive their external covering from the peritoneum, which becomes connected at their open extremity with the membrane which lines them. Between the external and internal membrane is the proper tissue of the tubes, and which, except in very muscular subjects, seldom display the fibrous structure; still, nevertheless, two layers of fibres have been observed--an outer or longitudinal, and an inner or circular layer. The Fallopian tubes are lined with mucous membrane, forming numerous longitudinal rugæ. The canal is not pervious during the early months of foetal life, the abdominal extremity being closed and rounded; this appears to open about the fourth month. The canal is relatively larger, the younger the embryo is, and may, therefore, be easily demonstrated at this time.
At the period of impregnation, the Fallopian tubes implant themselves by means of their fimbriated extremity upon that part of the ovary where the Graafian vesicle is about to burst; they become remarkably engorged with blood, assuming a deep purple colour, and are now much thicker; the canal enlarges, so that a tolerably-sized probe can be introduced, whereas, at other periods it will scarcely admit a large bristle. The uterine extremity of the tube is closed by a continuation of that pulpy coagulable lymph-like secretion which now lines the cavity of the uterus, forming the membrana decidua of Hunter, and which, especially on the side where the corpus luteum is found, extends into the tube to nearly the distance of an inch. The tubes are now observed to be in a state of distinct peristaltic motion, "like writhing worms," as Mr. Cruickshank has well expressed it; "the fimbriæ were also black and embraced the ovaria (like fingers laying hold of an object) so closely and so firmly, as to require some force and even slight laceration to disengage them."[6] From the great degree of vascularity which is observed in the Fallopian tubes at this period, some anatomists have been induced to consider that their proper tissue was vascular, analogous to the corpora cavernosa penis. Besides the peristaltic motion already mentioned, other movements called ciliary have been observed in the Fallopian tubes at this period, consisting of minute portions of mucous membrane moving briskly and whirling round their axis, apparently for the purpose of propelling the ovum.[7]
As pregnancy advances, the Fallopian tubes undergo other changes as respects their situation, which are worthy of notice. The broad ligaments, in the upper parts of which the Fallopian tubes take their course, are well known to be merely expansions of peritoneum from each side of the uterus, and therefore become gradually unfolded and shorter as the uterus increases in size. "In proportion as the fundus uteri rises upwards and increases in size, the upper part of the broad ligament is so stretched that it clings close to the side of the uterus, so that in reality the broad ligament disappears, no more of it remaining than its very root, viz. its upper and outer corner, where the group of spermatic vessels pass over the iliacs immediately to the side of the uterus. In this state, though the small end of the tube opens in the same part of the uterus as before impregnation, yet the tube has a very different direction. Instead of running outwards in the horizontal direction, it runs downwards, clinging to the side of the uterus. And behind the fimbriæ lies the ovarium, for the same reason clinging close to the side of the uterus."[8]
Uterus. The uterus is a hollow fibrous viscus situated in the hypogastric region between the bladder and the rectum, below the intestinum ileum and above the vagina, and is by far the largest of the generative organs. It is of a pyriform figure: its upper portion which is the largest is triangular, becoming gradually smaller inferiorly; that portion of it which is above the spot where the Fallopian tubes enter is called the fundus uteri; the lower and cylindrical portion receives the name of cervix; that between the cervix and fundus is called the body of the uterus.
The parietes of the adult uterus are nearly half an inch in their greatest thickness, which is about the middle of the body, the body being slightly thicker than the cervix, which is of a somewhat harder structure. Near the point at which the Fallopian tubes enter the uterus the parietes become thinner, gradually diminishing from four or five to only one line in thickness.
The cavity of the uterus is triangular, its base being directed upwards, the superior angles corresponding to the points where the Fallopian tubes enter it. The cavity of the uterus is so small, owing to the thickness of its parietes, that they are nearly in contact: it is only four lines in breadth; the fundus, which forms the base of the triangle, is convex both internally as well as externally; whereas, the sides which form the body are convex internally, but somewhat concave externally.
The cavity of the uterus is most contracted at the point where the cervix is united to the body, which here forms the os uteri internum; from this point the cervix gradually dilates as far as its middle portion, when it again contracts; its lower extremity terminates in the upper part of the vagina by an anterior and posterior cushion-like projection, of which the posterior is usually the longest, although from the direction of the uterine axis the anterior is commonly felt lowest in the pelvis. Between these there is a transverse fissure known by the name of os tincæ or os uteri externum, the lips or labia of which are formed by the two above-mentioned prominences. The internal surface of the body of the uterus is smooth, whereas that of the cervix is uneven, forming upon its anterior and posterior wall a number of delicate rugæ diverging obliquely in an arborescent form, and hence called the arbor vitæ. The lips of the os uteri are smooth, except when slight lacerations have taken place during labour.
In the virgin state the uterus is about two inches long, of which the cervix occupies the smaller half: the greatest breadth of the body is sixteen lines; that of the cervix from nine to ten. The uterus which has been impregnated, especially when this has been frequently the case, scarcely ever regains its original dimensions, and the fissure which the os tincæ forms becomes broader from before backwards. The weight of an adult virgin uterus is from seven to eight drachms, but the uterus which has been once impregnated is seldom less than an ounce and a half. It lies between the bladder and rectum, its upper half being covered by peritoneum, which closely adheres to it. In the adult state it is situated entirely in the cavity of the pelvis; the fundus, which is below the upper edge of the symphysis pubis, is turned forwards and upwards, while its mouth is directed downwards and backwards, so that its long axis is nearly parallel to the axis of the superior aperture of the pelvis.
The uterus is connected to the neighbouring parts by several duplicatures of peritoneum, which are continuous with that portion of it which covers the fundus. The most considerable are the broad or lateral ligaments: these arise from the sides of the uterus, which is enclosed between their anterior and posterior layers or laminæ; they proceed transversely outwards towards the sides of the pelvic cavity, which is thus divided into two portions, and are then continued into that portion of the peritoneum which lines the cavity.
The round ligaments arise from the sides of the uterus close beneath and a little anterior to the uterine extremity of the Fallopian tubes. They pass between the two layers of the broad ligaments, behind the umbilical arteries, and before the iliac vessels, in a direction upwards and outwards to the external opening of the inguinal canal; they then make a turn round the epigastric artery downwards, inwards, and forwards, and pass through the abdominal ring, and dividing into numerous fasciculi and fibres are gradually lost in the cellular substance of the mons Veneris and upper portion of the labia. Besides consisting of cellular substance and blood-vessels, the round ligaments contain some very distinct bundles of muscular fibres, of which the upper arise from the external layer of uterine fibres, and the lower from the inferior edge of the internal oblique muscle, and pass upwards.
Upon a superficial examination, the structure of the uterus would almost seem to be homogeneous, nevertheless a number of reddish yellow strata interspersed with whitish streaks running from behind forwards may be perceived even in the unimpregnated state; between these strata the vessels of the uterus take their course, forming numerous anastomoses.
There is much difference of opinion among anatomists as to the fibrous structure of the uterus. The majority however agree as to the presence of muscular fibres,[9] some considering that they always exist, while others, and by far the greater number, consider them as appearances peculiar to pregnancy: they are, it is true, extremely indistinct in the unimpregnated state, but they are far from being peculiar to pregnancy, as they are frequently developed by any circumstances by which the formative powers of the uterus are excited. Thus in cases where the uterus has been much distended by some anormal growth, its fibres become much developed and distinctly fasciculated. Lobstein observed them very distinctly in a uterus which had been distended to the size of a seven months' pregnancy by a fatty tumour.
The uterine fibres have been usually considered as fleshy, but they differ from the red fibres of voluntary muscles, in being of a paler colour, flatter, and remarkably interwoven with each other: nevertheless they appear to be really muscular fibres from the powerful contraction with which they expel the foetus and placenta, and nearly obliterate the cavity of the uterus. In the unimpregnated state they resemble the fibrous coat of an artery, whereas, those of the gravid uterus are more like the fibres of muscle. Most anatomists agree in describing two sets of fibres, viz. longitudinal and transverse. The external layer of fibres appears to form the round ligaments, which seem to have the same relation with them as tendon and muscle. "The fibres arise from the round ligaments, and regularly diverging spread over the fundus until they unite and form the outmost stratum of the muscular substance of the uterus. The round ligaments of the womb have been considered as useful in directing the ascent of the uterus during gestation, so as to throw it before the floating viscera of the abdomen: but in truth it could not ascend differently; and on looking to the connexion of this cord with the fibres of the uterus, we may be led to consider it as performing rather the office of a tendon than that of a ligament."[10] "On the outer surface and lateral part of the womb, the muscular fibres run with an appearance of irregularity among the larger blood-vessels, but they are well calculated to constringe the vessels, whenever they are excited to contraction. The substance of the gravid uterus is powerfully and distinctly muscular, but the course of the fibres is less easily described than might be imagined: this is owing to the intricate interweaving of the fibres with each other--an intermixture however which greatly increases the extent of their power in diminishing the cavity of the uterus. After making sections of the substance of the womb in different directions, we have no hesitation in stating that towards the fundus the circular fibres prevail, that towards the orifice the longitudinal fibres are most apparent, and that on the whole, the most general course of the fibres is from the fundus towards the orifice.
"This prevalence of longitudinal fibres is undoubtedly a provision for diminishing the length of the organ, or for drawing the fundus towards the orifice. At the same time these longitudinal fibres must dilate the orifice and draw the lower part of the uterus over the head of the child.
"In making sections of the uterus while it retained its natural muscular contraction, I have been much struck in observing how entirely the blood-vessels were closed and invisible, and how open and distinct the mouths of the cut blood-vessels became when the same portions of the uterus were distended or relaxed. This fact of the natural contraction of the substance of the uterus closing the smallest pore of the vessels, so that no vessels are to be seen, where we nevertheless know that they are large and numerous, demonstrates that a very principal effect of the muscular action of the womb is the constringing of the numerous vessels which supply the placenta, and which must be ruptured when the placenta is separated from the womb."
"Upon inverting the uterus, and brushing off the decidua, the muscular structure is very distinctly seen: the inner surface of the fundus consists of two sets of fibres, running in concentric circles round the orifices of the Fallopian tubes; these circles at their circumference unite and mingle, making an intricate tissue. Ruysch, I am inclined to believe, saw the circular fibres of one side only; and not adverting to the circumstance of the Fallopian tube opening in the centre of these fibres, which would have proved their lateral position, he described the muscle as seated in the centre of the fundus uteri. This structure of the inner surface of the fundus of the uterus is still adapted to the explanation of Ruysch, which was that they produced contraction and corrugation of the surface of the uterus, which, the placenta, not partaking of, the cohesion of the surface was necessarily broken. Farther, I have observed a set of fibres on the inner surface of the uterus, which are not described: they commence at the centre of the last described muscle, and having a course in some degree vortiginous, they descend in a broad irregular band towards the orifice of the uterus: these fibres co-operating with the external muscle of the uterus, and with the general mass of fibres in the substance of it, must tend to draw down the fundus in the expulsion of the foetus, and to draw the orifice and lower segment of the uterus over the child's head." (C. Bell, op. cit.)
There are other circumstances which prove the muscularity of the uterus, beyond the mere evidence of its fibres, as seen during pregnancy. "In the quadruped," as Dr. Hunter observes, "the cat particularly and the rabbit, the muscular action or peristaltic motion of the uterus is as evidently seen as that of the intestines, when the animal is opened immediately after death." It is also proved by the powerful contraction which it exerts during labour, and "by the thickness of the fibres corresponding with their degree of contraction." (Ibid.)
The inner surface of the uterus is lined by a smooth or somewhat flocculent membrane of a reddish colour, which is continued superiorly into the Fallopian tubes; inferiorly it becomes the lining membrane of the vagina.
Mucous follicles are only found in the cervix, especially at its lower part: when by chance these become inflamed, the orifice closes, and the follicle becomes more or less distended by a collection of thin fluid. The mucous casts of these follicles have been known by the name of ovula Nabothi, having been mistaken by an old anatomist for Graafian vesicles, which had been detached from the ovary, and conveyed into the cavity of the uterus.
The mucous membrane which lines the cervix uteri is corrugated into a number of rugæ, between which the mucous follicles are chiefly found.
Before quitting this subject, it will be necessary to point out the changes which the uterus presents at different periods of foetal life, and the great resemblance it has at these periods to the uterus, as it appears in the lower classes of the mammalia. We may, however, observe in the first place, that the uterus is not found to exist as a separate organ until we come to the class mammalia; and even in the lower genera of this class it bears a strong resemblance to the tubular character of the generative organs in the inferior classes of animal life. The nearest to the tubular uterus, and where the transition from the oviduct in birds, &c. to the uterus in mammalia is least distinctly marked, is in the uterus duplex. Although the uterus is double, there is but one vagina into which the two ora uteri open; its low grade of development is marked by the resemblance which each uterus bears to an intestinal tube: there are as yet no traces of a cervix, each os uteri merely forming a simple opening at the lower end of what is little more than a cylindrical canal. We do not find that thickening at the lower extremity of the uterus which distinguishes the cervix in the higher mammalia. This species of uterus is found among a large portion of the rodentia, and is also occasionally met with as an abnormal formation in the human subject. The next grade of uterine development appears under the form of the uterus bicollis. The double os uteri here ceases to exist, and the division begins a little higher up, so that the two cavities of the uterus communicate for a short space: the ova, however, do not reach the common cavity, but remain each in its separate cornu. In this form of uterus, the os uteri is not only single, but the lower portion is thickened, although it has not yet formed a distinct neck or cervix; it is met with among some of the rodentia, and also certain carnivora.
In the uterus bicorporeus, the union of the cornua is higher up, so that the lower portion is single, while the upper part alone is double, consisting of two strongly curved cornua. This conformation is peculiar to ruminating animals. If two ova be present they are separate from each other, each being contained in its own distinct body or cornu, but a portion of the membranes extends along the common cervix, from one body to the other.
A still higher grade is the uterus bifundalis, where the fundus alone is double, the cornu being formed only by this portion. This formation is observed in the horse, ass, &c.: the common cavity is here the receptacle of the ovum, so that in the unimpregnated state, the cornua appear only as appendices, into which a portion of the membranes extend.
In the uterus biangularis, the double formation has nearly disappeared, except at the fundus, where the uterus imperceptibly passes into the tubes: this is the case among the edentata, and some of the monkey tribes.
The highest grade is the uterus simplex: every trace here of the double form is lost; the fundus no longer forms an acute angle, where it bifurcates into two cornua; but is convex. We now for the first time see the divisions of the uterus into body and cervix distinctly marked.
The human uterus presents a similar variety of forms, as it gradually rises in the scale of development during the different periods of utero-gestation. It is at first divided into two cornua, and usually continues so to the end of the third month, or even later; the younger the embryo the longer are the cornua, and the more acute the angle which they form; but even after this angle has disappeared, the cornua continue for some time longer.
The uterus is at first of an equal width throughout; it is perfectly smooth and not distinguished from the vagina either internally or externally by any prominence whatever. This change is first observed when the cornua disappear and leave the uterus with a simple cavity. The upper portion is proportionably smaller, the younger the embryo is. The body of the uterus gradually increases, until at the period of puberty it is no longer cylindrical, but pyriform: even in the full-grown foetus the length of the body is not more than a fourth part of the whole uterus; from the seventh even to the thirteenth year it has only a third, nor does it reach a half until puberty has been fully attained. The os tincæ or os uteri externum first appears as a scarcely perceptible prominence projecting into the vagina; it increases gradually, in size until the latter months of gestation, when the portio vaginalis is relatively much larger than afterwards.
The parietes of the uterus are thin in proportion to the age of the embryo. They are of an equal thickness throughout at first: at the fifth month, the cervix becomes thicker than the upper parts; between five or six years of age, the uterine parietes are nearly of an equal thickness, and remain so until the period of puberty, when the body becomes somewhat thicker than the cervix.
As the function of menstruation with its various derangements will be considered among the diseases of the unimpregnated state, we proceed to consider these changes which the uterus undergoes during pregnancy as well as during and after labour: these are very remarkable both as regards its structure, form, and size.
Shortly after conception, and before we can perceive any traces of the embryo, the uterus becomes softer and somewhat larger, its blood-vessels increased in size, and the fibrous layers of which its parietes are composed looser and more or less separated. The internal surface when minutely examined has a flocculent appearance, and very quickly after conception becomes covered with a whitish paste-like substance, which is secreted from the vessels opening upon it; this pulpy effusion soon becomes firmer and more dense; it bears a strong analogy to coagulable lymph, and forms a membrane which lines the whole cavity of the uterus, and which in the course of a few weeks (from changes to be mentioned hereafter) crosses the os uteri and thus closes it. The uterine cavity in a short time becomes still farther closed by the canal of the cervix being completely sealed, as it were, by a tough plug of gelatinous matter which is secreted by the glandules of that part.
The structure of the uterus becomes remarkably altered; its fibrous structure is much more apparent; in fact, it is only during pregnancy, or when the uterus has been distended by some anormal growth, that we are able to detect the uterine fibres with any degree of certainty. This has led some anatomists to consider that they are only formed at such periods, a supposition which is not very probable; at any rate they now become very distinct: hence the uterus does not owe its increasing size to mere extension, but it evidently acquires a considerable increase of substance, a fact which is not only proved by examining the contracted uterus after labour at the full period, but also by comparing its weight with that of the unimpregnated organ. The adult virgin uterus weighs about one ounce, whereas the gravid uterus at the full term of pregnancy, when emptied of its contents, weighs at least twenty-four ounces, showing that there has been an actual increment of substance in the proportion of one to twenty-four. Having ascertained this point, it next becomes a question, whether the parietes of the gravid uterus increase in thickness during pregnancy, or whether they become thinner. Meckel, who is one of the greatest modern authorities on these subjects, states that from careful admeasurement of sixteen gravid uteri at different periods of gestation, he finds the parietes become thicker during the first, second, or third months, but after this period they become gradually thinner up to the full time: they are thicker in the upper parts of the uterus, whereas inferiorly they are a third or nearly a half less.
Nothing proves the actual increase of bulk and substance in the uterus more than its appearance when contracted immediately after labour at the full term; it forms a fleshy mass as large as the head of a new-born child, the parietes of which are at least an inch in thickness.
"The spongy or cellular tissue (says M. Leroux) becomes considerably developed during pregnancy, and its porous cells increase in proportion as the uterus dilates, more especially at the fundus and the spot where the placenta is attached, where they become so large as to admit a goosequill. The internal membrane is pierced with numerous orifices, of which some are the mouths of arteries, and others communicate with the cells already mentioned. This membrane also during pregnancy forms those irregular tufted rugæ, which serve to give a more intimate connexion between the uterus and the placenta. In the unimpregnated uterus and in the intervals between the menstrual periods the little orifices which are observed in the lining membrane of the uterus contain only a transparent lymph, which lubricates the interior of the uterus; during the appearance of the menses they contain blood, and during pregnancy they are connected with the vessels of the placenta and chorion."[11]
There is no circumstance in which the gravid uterus differs more from the unimpregnated than in the size and termination of its blood-vessels. The arteries, both spermatic and hypogastric, are very much enlarged. The hypogastric is commonly considerably larger than the spermatic, and we very often find them of unequal sizes in the different sides. They form a large trunk of communication all along the side of the uterus, and from this the branches are sent across the body of the uterus both before and behind. The cervix uteri has branches only from the hypogastrics, and the fundus only from the spermatics; or, in other words, the hypogastric artery gives a number of branches to the cervix, besides sending up the great anastomosing branch, and the spermatic artery supplies the tube and fundus uteri before it gives down the anastomosing branch on the lateral parts of the uterus. All through the substance of the uterus there are infinite numbers of arteries large and small, so that the whole arterial system makes a general network, and the arteries are convoluted or serpentine in their course.[12] Hardly any of the larger arteries are seen for any length of way upon the outside of the uterus. As they branch from the sides where they first approach the uterus, they disappear by plunging deeper and deeper into its substance.
The arterial branches which are most enlarged are those which run towards the placenta, so that wherever the placenta adheres, that part appears evidently to receive by much the greatest quantity of blood, and the greatest number both of the large and small arteries at that part pass through to the placenta, and are necessarily always torn through upon its separation. The veins of the uterus would appear to be still more enlarged in proportion than the arteries. The spermatic and hypogastric veins in general follow the course of the arteries, and like them anastomose on the side of the uterus. From thence they ramify through the substance of the uterus, running deeper and deeper as they go on, and without following precisely the course of the arterial branches. They form a plexus of the largest and most frequent communications which we know of in the vessels of the human body, and this they have in common with the arteries that their larger branches go to, or rather come from, that part of the uterus to which the placenta adheres: so that when the venous system of the uterus is well injected, it is evident that that part is the chief source of returning blood. Here, too, both the large and small veins are continued from the placenta to the uterus, and are always necessarily broken, upon the separation of these two parts. As I know no reason for calling the veins of the uterus sinuses, and as that expression has probably occasioned much confusion among the writers upon this subject, I have industriously avoided it.[13]
The form of the uterus changes considerably during pregnancy: the upper part appears to increase in greater proportion than the lower, a fact which appears to be proved from the alteration which takes place in the relative position of the Fallopian tubes, which are situated much lower down the sides of the uterus at full term than in the unimpregnated state, nor do they entirely regain their former position after labour, until the female has attained an advanced age; hence as the cervix diminishes in length during the latter half of pregnancy, it follows that the difference in point of size between the fundus and the body of the uterus, and this part will be continually increasing.
As the uterus increases, the fundus of course rises and can be felt through the distended abdominal parietes: its anterior surface, especially in the latter month of pregnancy, lies immediately behind the anterior wall of the abdominal cavity, and pushes the small intestines upwards, backwards, and to the sides.
The form of the gravid uterus differs also from that in the unimpregnated state in other respects, and this difference appears to depend in great measure upon its increase of size, and upon the form of the cavities which it occupies. Thus in the unimpregnated state when it occupies the cavity of the pelvis, its anterior surface which corresponds to the bladder is flattened; whereas its posterior surface, which is turned towards the hollow of the sacrum, is convex; it is however the reverse during the latter half of pregnancy. The anterior surface is now strongly convex, being merely covered by the yielding anterior wall of the abdomen; whereas posteriorly the uterus is nearly concave, corresponding to the solid convexity of the lumbar vertebræ, a fact which may be easily ascertained by examining the abdomen of a patient in the last month of pregnancy while lying down. The situation and position of the uterus are also changed in the unimpregnated state; the fundus is inclined somewhat backwards, the os uteri being nearly in the centre of the pelvic cavity, but the gravid uterus during the latter half of pregnancy has its fundus strongly inclined forwards and the os uteri directed backwards towards the upper part of the hollow of the sacrum.[14]
A minute and intimate knowledge of the changes and appearances which the uterus presents at every period of pregnancy, is essential to the diagnosis and treatment of the various derangements to which this process is subject. The numerous and important questions in medical jurisprudence connected with pregnancy can alone be determined by its means; and it is only by more close and attentive observation of every step in the gradual development of the uterus up to the full term of gestation, that we can expect to increase our means of forming a correct and certain diagnosis in those cases of doubtful pregnancy, where not merely professional reputation is more or less at stake, but the character, happiness, and even life of the individual upon whose case we are required to decide.
During the first month of pregnancy the changes are not very appreciable upon examination during life. The uterus has become larger, softer, and more vascular, much as it does during a menstrual period. The portio vaginalis of the cervix, which in the unimpregnated state is hard and almost cartilaginous to the feel, becomes softer and larger:[15] the transverse fissure which the os uteri forms is more oval.
In the second month, the abdomen becomes somewhat flat: the portio vaginalis can be now reached by the finger with greater ease than at any time of pregnancy, which is not from the uterus itself being lower in the pelvis, but from not yet having altered its position; any increase of its size therefore will cause its inferior extremity to be felt lower down and nearer to the os externum. The os uteri has undergone a considerable change, inasmuch as its edges have lost their lip-like figure; they now form a ring or rather dimple-like concavity at the lower end of the cervix, its canal being closed by the gelatinous plug already mentioned.
In primiparæ, or women pregnant for the first time, the margin of the os uteri thus closed is not only circular but perfectly smooth; whereas in multiparæ, not only is the cervix usually larger in every direction, but the os uteri itself is larger, thicker, and of an irregular shape; it is also knotty here and there from little callous cicatrices, where its edge has been torn in former labours.
In the third month of pregnancy the uterus rises above the brim of the pelvis. A slight protrusion of the abdomen may be sometimes observed above the pubes; the os uteri is not reached so easily as in the preceding month. The alteration which takes place in the situation of the uterus during the third month appears to result from gradual shortening of the broad ligament as it increases in size. As the uterus rises it pushes up that portion of the small intestines which rests upon it; these however being confined by the mesentery to the spine, and therefore prevented ascending before the uterus, at length slip down behind it, and the fundus being freed from the superincumbent pressure rises in a direction upwards and forwards into the cavity of the abdomen. The direction of the uterus becomes much altered; the os uteri is no longer in the middle of the pelvic cavity, but inclines towards the upper part of the hollow of the sacrum, whereas the fundus approaches more and more to the anterior parietes of the abdomen.
In the fourth month, the fundus uteri has risen about two or three fingers' breadth above the symphysis pubis; this is not very easily ascertained even in a thin person, still less where the patient is stout and the parietes of the abdomen therefore thick. The directions which the celebrated Roederer has given for making an examination of the abdomen during the early months of pregnancy, are well worthy of notice. Having evacuated the bladder and rectum, the patient should be placed in a half-sitting posture with the knees drawn up, so as to relax the abdominal parietes as much as possible: she must then breathe slowly and deeply; and if the hand be suddenly pressed against the abdomen a little above the symphysis pubis, at the moment of her making a full expiration, we shall in all probability feel the hard globe of the uterus.
In the fifth month, the fundus will be felt half way, or a little more, between the symphysis pubis and umbilicus. The increased size of the abdomen cannot be concealed by the dress; the portio vaginalis has become distinctly shorter, and the os uteri is situated higher in the pelvis and more posteriorly.
In the sixth month, the fundus has risen as high as the umbilicus; the irregular folds of the skin which form the fovia umbilici or navel depression begin to disappear; the first perceptible movements of the child may occasionally be felt; the portio vaginalis has lost half its length, being scarcely half an inch in length.
In the seventh month, the fundus rises an inch or so above the umbilicus, the folds of which have nearly disappeared. In some cases it begins to protrude, forming a species of umbilical hernia: this varies a good deal in different individuals, being more marked in primiparæ; whereas in women, whose abdomen has been distended in previous pregnancies, little or no convexity of the navel is produced until a later period, and not always even then, the umbilical depression being merely diminished in point of depth, and its folds not so strongly marked. The movements of the child are now perfectly distinct; the portio vaginalis is still shorter, and approaches more and more to the upper part of the hollow of the sacrum. The anterior portion of the inferior segment of the uterus, or that part which extends from the os uteri towards the symphysis pubis, is now considerably developed and convex, and on pressing the point of the finger against it, the presenting part of the child will be felt. When this is the head as is usually the case, it will feel like a light ball which rises when pushed by the finger, but which, if the finger be held still, in a few moments descends and may again be felt.
In the eighth month, the fundus has risen half way between the umbilicus and the scrobiculus cordis. The abdomen has increased considerably in size, and has become more convex; the umbilical depression in primiparæ has entirely disappeared. The portio vaginalis is still shorter, being barely a quarter of an inch in length. The os uteri is so high up as not to be reached without difficulty; the presenting part of the child can be distinctly felt.
In the ninth month, the fundus has reached nearly to the scrobiculus cordis, and by the end of the month is quite in it; this is more especially the case with primiparæ: the anterior parietes of the abdomen not allowing the fundis to incline so strongly forwards, the oppression of breathing is therefore more marked in them than in multiparæ, for the fundus uteri rising so high prevents in great measure the action of the diaphragm, so that the chest is expanded by other muscles; hence the shortness of breath and inability of moving, so frequently complained of at this period of utero-gestation. The portio vaginalis is still shorter, and in the primipara forms little more than a soft cushiony ring which marks the os uteri. The inferior part of the uterus is becoming more spherical, and is usually occupied by the presenting part of the child: this latter is no longer so moveable as before, its size as also its weight being evidently increased. That portion of the uterus which extends between the symphysis pubis and os uteri is now not only more convex but lower in the pelvis than the os uteri itself.
During the last four weeks of pregnancy a considerable change is observed. The fundus is now lower than it was in the preceding month, being about half way between the scrobiculus cordis and umbilicus; the abdomen has, as it is called, fallen; and from the diaphragm being now able to resume its functions the breathing becomes more easy, and the female feels more comfortable and capable of moving about. On examination per vaginam the anterior portion of the inferior segment of the uterus will be felt still deeper in the pelvis: if the head presents it distends this part of the uterus, so that, in many cases, we have to pass the finger round it before we can reach the os uteri, which is now in the upper part of the hollow of the sacrum. All traces of the cervix have now disappeared, it having been required to complete the full development of the uterus; the situation of the os uteri itself is marked merely by a small depression or dimple; there is no longer any distinction between the os uteri internum and externum; the edges of the opening are so thin as to be nearly membranous, but remain closed in primiparæ until the commencement of labour.[16]
In women who have had several children, a considerable difference is observed as regards the state of the cervix and os uteri: the cervix does not undergo that shortening during the latter half of pregnancy, which is the case in a primipara, a portion of it at least remaining up to the full term of utero-gestation: in many cases, especially where the female has had a large family, it is nearly an inch long at this period; nor is the lower portion of the uterus so spherical as in the primipara; to this circumstance may probably be attributed the fact of the head not descending so deep into the pelvis just before labour. In multiparæ the os uteri is also very different: instead of being perfectly round with its edges smooth, it is irregular and uneven, and seldom loses altogether the lip-like shape of the unimpregnated state in consequence of the greater thickness and elongation of its lips from former labours; its edges here and there is uneven and knotty, from little callous cicatrices, where it has been torn; moreover it does not remain closed till the commencement of labour, but the os uteri externum (commonly called os tincæ,) and sometimes even the os uteri internum will be more or less open during the last three or four weeks of pregnancy. These peculiarities are of great importance in coming to a conclusion as to whether a patient be in her first pregnancy or not: although not invariable in the utmost sense of the word, still their occurrence, even after a single labour, is sufficiently frequent to make them worthy of careful observation. Indeed, on more than one occasion, we have known them occur even after a miscarriage, a circumstance on the strength of which the patient had ventured to deny that she was pregnant. On the other hand, we sometimes meet with the os uteri in a second pregnancy so little altered by the effects of the previous labour, that it would be extremely difficult to come to a decision.
When labour is over, the uterus contracts very considerably, and, in a few days after, its parietes will be found at least an inch in thickness. It now gradually diminishes in size, and continues to do so for some weeks; the blood-vessels contract, and losing the peculiarly loose spongy structure of pregnancy it becomes harder, firmer, and more compact. It nevertheless remains softer and larger than in the virgin state, and does not attain its original size and hardness until an advanced period of life.
The os uteri, which in the latter months of pregnancy had formed a circular opening, resumes its former shape, except that its lips, especially the posterior one, which are more or less irregular and uneven, are thicker and longer than in the virgin state. For the first weeks after labour, the os uteri is high in the pelvis, soft, and easily admits the tip of the finger; at the end of the second week it is much lower in the pelvis, and no longer permits the finger to pass. Immediately after labour, the contracted uterus forms a hard solid ball, the size of a new-born child's head; this state of contraction is not, however, of long continuance: in the course of half an hour, or even less, it begins to increase in size, becoming softer and larger, and continuing to increase slowly for some hours, when it again gradually diminishes, until, as before observed, it approaches its original size in the unimpregnated state. The state of powerful contraction in which the uterus is felt immediately after labour, after a time gradually relaxes; its spongy texture, from which the blood had been forcibly expelled by the violent action of its fibres, becomes again filled with blood; the organ swells and becomes softer and more bulky, and the orifices of the vessels which open into the cavity of the uterus are again partly pervious, and emit a sanious fluid called the lochia. This state lasts for two or more days after delivery, when the vessels begin to recover their former caliber, and lose that degree of dilatation peculiar to the gravid state. The lochia become less and less coloured, and now, and not before the uterus undergoes that gradual diminution of size and bulk which we have just alluded to.
The copulative or external organs of generation are the vagina, hymen, clitoris, nymphæ, and labia, the three last being known by the term vulva.
Vagina. The vagina is a canal of about four inches in length and one in breadth, broader above than below; its parietes are thin and are immediately connected with the uterus. It envelopes the portio vaginalis of the uterus at its upper or blind extremity (fundus vaginæ,) and is continuous with its substance; inferiorly, where it is narrowest, it passes into the vulva. It is situated between the bladder and rectum, and attached to each by loose cellular tissue. Its direction differs from that of the uterus, for its axis corresponds very nearly with that of the pelvic outlet, running downwards and forwards. Posteriorly it is somewhat convex, anteriorly concave.
The vagina consists of two layers; the external, which is very thin, firm, of a reddish-white colour, and continuous with the fibrous tissue of the uterus; and a lining mucous membrane which is closely united to it. This latter is much corrugated, especially in the virgin state, the rugæ running transversely in an oblique direction, and gathered together on its anterior and posterior surface, forming the columna rugarum anterior and posterior, which appear to be a continuation of the corrugations which form the arbor vitæ of the cervix.
In the upper part of the vagina there are considerable mucous follicles, which moisten the canal with their secretion, and which during sexual intercourse, and particularly during the first stage of labour, pour forth an abundant supply of colourless mucus for the purpose of lubricating the vagina, and rendering it more dilatable. Near its orifice, especially at the upper part, the veins of the vagina form the plexus retiformis, a congeries of vessels which has almost a cellular appearance, and from this reason has been called the corpus cavernosum of the vagina; it appears to be capable of considerable swelling from distension with blood, like the corpus cavernosum penis, and by this means serves to contract still farther the os externum during the presence of venereal excitement. A similar disposition to form plexuses of vessels is seen in the venous circulation of the nymphæ, bladder, and rectum.
Hymen. The lining membrane of the vagina is of a reddish-gray colour, interspersed here and there, especially at its upper part, with livid spots like extravasation. At the os externum it forms a fold or duplicature called hymen, running across the sides of the posterior part of the opening, and usually of a crescentic figure, the cavity looking upwards. The duplicatures of membrane are united by cellular tissue. In some instances, the hymen arises from the whole circumference of the os externum, having a small orifice in the centre for the escape of the menses and vaginal secretions: in some rare cases it is cribriform; and in others it completely closes the vaginal entrance. When torn in the act of sexual intercourse, it generally forms three or four little triangular appendages, called carunculæ myrtiformes, arising from the posterior and lateral portions of the os externum.
From the identity of its fibrous coat with that of the uterus, the vagina possesses considerable powers of contraction, when excited by the presence of any body which distends it; hence it is a valuable assistance to the uterus during labour: it also stands in the same relation to the abdominal muscles that the rectum does, so that as soon as it is distended by the head, &c. it calls them into the strong involuntary action, which characterizes the bearing down pains of the second stage of labour. The orifice of the vagina (os externum) is surrounded by a thin layer of muscular fibres, which arise from the anterior edge of the sphincter ani; they enclose the outer margin of the vagina, cover its corpus cavernosum, and are inserted into the crura clitoridis at their union. It has been called the sphincter or constrictor vaginæ, and assists the corpus cavernosum still farther in contracting the os externum.
Clitoris. The clitoris is an oblong cylindrical body, situated beneath the symphysis pubis, arising from the upper and inner surface of the ascending rami of the ischium, by means of two crura of about an inch long, and uniting with each other at an obtuse angle. It terminates anteriorly in a slight enlargement, called the glans clitoridis, which is covered with a thin membrane or a loose fold of skin, viz. the preputium clitoridis. It is a highly nervous and vascular organ, and like the penis of the male, is composed of two crura and corpora cavernosa, which are capable of being distended with blood; they are contained in a ligamentous sheath, and have a septum between them. The clitoris is also provided with a suspensory ligament, by which it is connected to the ossa pubis. Like that of the penis, the glans clitoridis is extremely sensible, but has no perforation. Upon minute examination, it will be found that the gland is not a continuation of the posterior portion of the clitoris, but merely connected with it by cellular tissue, vessels, and nerves; the posterior portion terminates on its anterior surface in a concavity which receives the glans. In the glans itself there is no trace of the septum, which separates the corpora cavernosa. On the dorsum of the clitoris several large vessels and nerves take their course, and are distributed upon the glans, and upon its prepuce are situated a number of mucus and sebaceous follicles.
The crura clitoridis at their lower portion are surrounded by two considerable muscles, called the erectores clitoridis, arising by short tendons close beneath them from the inner surface of the ascending ramus of the ischium, and extending nearly to their extremity.
Nymphæ. The nymphæ or labia pudendi interna, are two long corrugated folds, resembling somewhat the comb of a cock, arising from the prepuce and glans clitoridis, and remaining obliquely downwards and outwards along the inner edge of the labia, increasing in breadth, but suddenly diminishing in size. At their lower extremity they consist of a spongy tissue, which is more delicate than that of the clitoris, but resembles considerably that of the glans, of which it appears to be a direct continuation. It has been called the corpus cavernosum nympharum, and is capable of considerable increase in size when distended with blood. The two crura of the prepuce terminate in their upper and anterior extremities; they are of a florid colour, and in their natural state they are contiguous to, and cover the orifice of the urethra. The skin which covers them is very thin and delicate, bearing a considerable resemblance to mucous membrane, especially on their inner surface, where it is continuous with the vagina; externally it passes into the labia.
The space between the nymphæ and edge of the hymen is smooth, without corrugation, and is called vestibulum.
Close behind the clitoris, and a little below it, is the orifice of the urethra, lying between the two nymphæ: it is surrounded by several lacunæ or follicles of considerable depth, secreting a viscid mucus; its lower or posterior edge is, like the lower portion of the urethra, covered by a thick layer of cellular tissue, and a plexus of veins, which occasionally become dilated and produce much inconvenience; it is this which gives the urethra the feel of a soft cylindrical roll at the upper part of the vagina; and in employing the catheter, by tracing the finger along it, the orifice will be easily found.
Labia. The labia extend from the pubes to within an inch of the anus, the space between the vulva and anus receiving the name of perineum.
The opening between the labia is called the fossa magna: it increases a little in size and depth, as it descends, forming a scaphoid or boat-like cavity, viz. the fossa navicularis.
The labia are thicker above, becoming thinner below, and terminate in a transverse fold of skin, called the frænulum perinei, or fourchette, the edge of which is almost always slightly lacerated in first labours. They are composed of skin cushioned out by cellular and fatty substance, and lined by a very vascular membrane, which is thin, tender, and red, like the inside of the lips; they are also provided with numerous sebaceous follicles, by which the parts are kept smooth and moist.
III. DEVELOPMENT OF THE OVUM
Membrana decidua.--Chorion.--Amnion.--Placenta.--Umbilical cord.--Embryo.--Foetal circulation.
Membrana decidua. The earliest trace of impregnation which is to be observed in the cavity of the uterus, and even before the ovum has reached it, is the presence of a soft humid paste-like secretion, with which the cavity of the uterus is covered, and which is furnished by the secreting vessels of its lining membrane. This is the membrana decidua of Hunter: properly speaking, it should be called the maternal membrane, in contra-distinction to the chorion and amnion, which, as belonging peculiarly to the foetus, are called the foetal membranes.[17]
Although at first in a semi-liquid state, it soon becomes firmer and more compact, assuming the character of a membrane: it appears to be nothing else than an effusion of coagulable lymph on the internal surface of the uterus, having "scarcely a more firm consistence than curd of milk or coagulum of blood." (Hunter, op. cit. p. 54.) Hence, although much thicker than the other membranes, it is weaker; it is also much less transparent.
It is not of an equal thickness, being considerably thicker in the neighbourhood of the placenta than elsewhere; inferiorily, and especially near the os uteri, it becomes thinner: during the first weeks of pregnancy it is much thicker than afterwards, becoming gradually thinner as pregnancy advances, until it is not half a line in thickness. In the earlier months its external surface is rough and flocculent, but afterwards it becomes smoother as its inner surface was at an earlier period.
It is much more loosely connected with the uterus during the first months of pregnancy than afterwards, and this is one reason why premature expulsion of the ovum is more liable to take place at this period than during the middle and latter part of utero-gestation. It is more firmly attached to the uterus in the vicinity of the placenta than any where else, which is owing to the greater number of blood-vessels it receives from the uterus at this point; whereas commonly "it has no perceptible blood-vessels at that part which is situated near the cervix uteri," (Ibid.,) this portion being much more loosely connected with the uterus. The course which the decidual vessels take on coming from the inner surface of the uterus is admirably adapted to render the attachment of this membrane to it as firm as possible.
Upon examining the lining membrane of the uterus at a very early period, when the decidua was still in a pulpy state, Professor v. Baer observed[18] that its villi, which in an unimpregnated state are very short, were remarkably elongated: between these villi, and passing over them, was a substance, not organized but merely effused, and evidently the membrana decidua at an extremely early age. The uterine vessels were continued into this substance, and formed a number of little loops round the villi, thus anastomosing with each other. On account of this reticular distribution it was impossible to distinguish arteries from veins; there is evidently the same relation between the uterus and the decidua as between an inflamed surface and the coagulable lymph effused upon it.
Professor v. Baer considers that at a later period the connexion between the decidua and mucous membrane becomes so intimate, that it is impossible to separate the former without also separating the latter from the fibrous tissue of the uterus. This, we apprehend, is the stratum which, as Dr. Hunter observes, "is always left upon the uterus after delivery, most of which dissolves and comes away with the lochia." He does not appear to have been fully aware of the close connexion between the decidua and lining membrane of the uterus, although he evidently observed the fact from the following sentence: "in separating the membranes from the uterus we observe that the adhesion of the decidua to the chorion, and likewise its adhesion to the muscular fibres of the uterus, is rather stronger than the adhesion between its external and internal stratum, which, we may presume, is the reason that in labour it so commonly leaves a stratum upon the inside of the uterus." According to the observations of Dr. Montgomery, a great number of small cup-like elevations may be seen upon the external surface of the decidua vera, "having the appearance of little bags, the bottoms of which are attached to, or embedded in, its substance; they then expand or belly out a little, and again grow smaller towards their outer or uterine end, which, in by far the greater number of them, is an open mouth when separated from the uterus: how it may be while they are adherent, I cannot at present say. Some of them which I have found more deeply embedded in the decidua were completely closed sacs. They are best seen about the second or third month, and are not to be found at the advanced periods of gestation."[19]
The membrana decidua does not envelope the ovum with a single covering, but forms a double membrane upon it, somewhat like a serous membrane; in fact, the descent of the ovum through the Fallopian tube is very similar to that of the testicle through the inguinal canal into the scrotum. The ovum pushes before it that portion of the decidua which covers the uterine extremity of the Fallopian tube, and enters the cavity of the uterus, which is already lined with decidua, covered by the protruded portion which forms the decidua reflexa. It must not be supposed that this reflexion of the decidua is completed as soon as the ovum enters the uterine cavity; the ovum usually remains at the mouth of the Fallopian tube, from which it has emerged, covered by the plastic mass of soft decidua, and the reflexion of this membrane will take place in proportion as the ovum gradually increases in size. The external layer of decidua is called decidua vera; the internal or reflected portion is called the decidua reflexa, having received this appellation from its discoverer, Dr. Hunter. These membranes would, as Dr. Baillie has correctly observed, be more correctly named the decidua uteri and decidua chorii: the decidua chorii or reflexa is reflected inwardly from above downwards; it is connected on its inner surface with the chorion: externally it is unattached, whereas, the decidua uteri or vera is unconnected on its inner surface, but attached to the uterus externally.
The membrana decidua differs in its arrangement from that of a serous membrane, inasmuch, as it is not only reflected so as to cover the chorion, but at the point of reflexion it is continued over the chorion externally, where it forms the placenta, so that the chorion is enclosed in all directions by the decidua: this latter portion, however, is not formed till about the middle of pregnancy. The decidua uteri or vera does not extend farther than the os uteri internum, which is filled up by the plug of tough gelatinous substance above described; the decidua chorii or reflexa, from its forming the outer covering of the chorion, of course passes over the os uteri.
According to Mr. John Hunter, the decidua vera is continued some little way into the Fallopian tubes, more especially, on that side where the corpus luteum has been formed; it is perforated at the points where the Fallopian tubes enter, as well as at the os uteri, a fact which is beautifully shown in Dr. Hunter's last plate: but this does not continue long, for, as Mr. John Hunter observes, the inferiour opening becomes closed in the first month, and, according to Lobstein's observations, the openings of the Fallopian tubes are closed after the second month. "Where the decidua reflexa is beginning to pass over the chorion, there is, at an early period of pregnancy, an angle formed between it and the decidua, which lines the uterus; and here the decidua is often extremely thin and perforated with small openings so as to look like a piece of lace.
"In proportion as pregnancy advances, the decidua reflexa becomes gradually thinner and thinner, so that at the fourth month it forms an extremely fine layer covering the chorion; it comes at the same time more and more closely in contact with the decidua, which lines that part of the uterus to which the placenta is not fixed, till at length they adhere together."[20] That portion of the decidua which passes between the placenta and uterus during the latter half of gestation, is called the placental decidua, the description of which will be given with that of the placenta.
To Dr. W. Hunter are we indebted for the first correct description of the decidua; indeed, so excellent is it, that the membrane has been called after him, the decidua of Hunter. Although he was the undoubted discoverer of the reflexa, the existence of the decidua was distinctly noticed by Burton, in 1751. In stating the post mortem examination of a woman, who died undelivered at the full time of pregnancy, he says, "Upon wiping the inside of the uterus very gently with a sponge, there seemed to be pieces of a very tender thin transparent membrane adhering to it in such parts of the uterus where the placenta did not stick to it; but as the womb was somewhat corrupted, and the membrane so very tender, we could not raise any bulk of it so as to be certain what it was." (Burton's Midwifery.)
The decidua seems chiefly intended to form the maternal part of the placenta: (see Placenta:) hence in all those quadrupeds when the maternal part of the placenta is permanently appended to the internal surface of the uterus, no decidua is found.
Having described the maternal membranes of the ovum, we come now to the membranes which form the parietes of the ovum. These are called the foetal membranes, for they are essentially connected with the origin of the foetus itself. They are the chorion and the amnion; besides which, there are two others that require notice, viz. the vesicula umbilicalis and allantois.
Chorion. The chorion is the proper covering of the ovum, and corresponds to the membrane lining the shell of an egg, in oviparous animals. It is a thin and transparent membrane, and presents on its external surface a ragged tufted appearance, being covered externally with groups of arborescent villous processes, which after a time unite into trunks to form the umbilical vessels, which, according to Lobstein's observations, are merely veins during the early period of gestation. These loose tufts of venous radicles appear to absorb nourishment for the ovum, much in the same manner as the roots of a plant. Although the chorion is so thin and transparent, it consists nevertheless of two laminæ or layers, between which the villi, which produce this shaggy appearance, take their course. Although the chorion on its external surface is nothing but a net-work of villi, which in process of time become vascular, anatomists have been unable to detect blood-vessels in the structure of the membrane itself. Its vascularity, however, has been asserted chiefly on the ground of the known vascularity of the decidua, it being supposed that the vessels of the decidua penetrate into the chorion. The chorion, however, belongs so essentially and exclusively to the foetus, that it appears extremely improbable that any maternal vessels should ramify in its structure for the purposes of its nourishment and growth, and the more so when we reflect that the nutrition of the foetus itself at this early period is obtained in so different a manner. It is, moreover, extremely difficult to distinguish between the venous absorbing radicles of the chorion, which form the early rudiments of the umbilical vessels, and any vessels which may take their course in the structure of the membrane itself; and the more we consider the relation between the chorion and the decidua, the less are we inclined to accept Meckel's explanation of the vascularity of the chorion, viz. that the vessels of the decidua have the same relation to those of the chorion as the blood-vessels of the maternal part of the placenta have to those of the foetal part.
Neither nerves nor lymphatics have been discovered in the structure of the chorion, unless, indeed, those white filaments, which are observed here and there about the edge of the placenta, perform the office of lymphatics. This has been hinted at by Dr. Hunter, where he says, "these are the remains of those shaggy vessels which shoot out from the chorion in a young conception, and give the appearance of the ovum being altogether surrounded by the placenta at that time. With a magnifying glass, they appear to be transparent ramifying vessels, which run in corresponding furrows upon the internal surface of the decidua, and a good deal resemble lymphatics." (W. Hunter, op. cit. p. 53.)
The chorion undergoes various changes during the different periods of pregnancy, and forms a very important part of the physiology of utero-gestation. Its thickness, which in the earlier months of pregnancy is more considerable than afterwards, at this period is uniform in every part of the ovum: its external surface covered with those villous prolongations which have already been alluded to. In the second month of pregnancy these become larger, and much more arborescent; after the third month a considerable portion of them gradually disappears, generally from below upwards, so that the greater part of its external surface becomes nearly smooth, except at that point where the umbilical cord has its origin, at which spot the villous prolongations become more developed, and unite to form the umbilical vessels. This part of the chorion, together with the corresponding portion of the membrana decidua, forms a flat circular mass, which at the end of pregnancy covers nearly one-third of the surface of the ovum, and constitutes the placenta or after-birth. At this point the chorion, which forms its inner surface, is considerably thicker than elsewhere.
At the commencement of pregnancy the chorion is but loosely connected with the decidua, but by degrees it becomes so closely connected by fibres, which are the remains of the little vascular prolongations, especially where these two membranes combine to form the placenta, that in the latter months of pregnancy, they can scarcely, if at all, be separated.
For the more minute consideration of the formation, development, and functions of the chorion, we must refer to the description of the placenta and foetus.
Amnion. The amnion is the inner membrane of the ovum. It is transparent, and of great tenuity, "yet its texture is firm, so as to resist laceration much more than the other membranes." (W. Hunter, op. cit. p. 50.) It is loosely connected with the chorion on its external surface, except when this membrane unites with the decidua to form the placenta at which spot it adheres to the chorion much more firmly. Its inner surface, which is in immediate contact with the liquor amnii, is very smooth; whereas externally, from being connected with the chorion by an exceedingly fine layer of cellular tissue, its surface is not so smooth. Dr. W. Hunter considers that this intervening tissue, is a gelatinous substance: it seems, however, to possess too much elasticity for such a structure; and, from the reticular appearance which it generally presents upon the membranes to which it adheres, we are inclined to adopt the opinion of Meckel in considering it cellular. "In the very early state of an ovum the amnium forms a bag, which is a good deal smaller than the chorion, and, therefore, is not in contact with it." (Ibid. p. 75:) hence, therefore, a space is formed between the two membranes which is filled with a fluid called the liquor amnii spurius, or more correctly the liquor allantoidis. "In the course of some weeks, however, it comes nearly into contact with the chorion, and through the greater part of pregnancy the two membranes are pretty closely applied to each other." (Ibid.) Lobstein, in his admirable Essai sur la Nutrition du Foetus, observes, that the membranes continues separate from each other so late as the third and fourth month. Cases every now and then occur where a considerable quantity of fluid is found between the chorion and amnion in labour at the full period of pregnancy.
We shall defer the minute description of the amnion and its relations, during the very early periods of utero-gestation, until we describe the embryo. The amnion is reflected upon the umbilical cord at its insertion into the placenta, envelopes the umbilical vessels, the external covering of which it forms, and is continued to the anterior surface of the child's abdomen, passing into that projecting portion of the skin which forms the future navel.
Blood-vessels and nerves have not as yet been discovered in the structure of the amnion, but Meckel considers it extremely probable that the fine layer of cellular tissue by which it is connected with the chorion contains vessels for its nutrition.
Liquor amnii. The amnion contains a fluid known by the name of liquor amnii. In the earlier months of pregnancy it is nearly, if not quite transparent; as pregnancy advances it becomes turbid, containing more or less of what appears to resemble mucus: it has a distinctly saline taste; its specific gravity is rather more than that of water. Its relative and absolute quantity vary considerably at different periods of pregnancy: thus the relative weight of liquor amnii to that of the foetus is very considerable at the beginning of pregnancy, at the middle they are nearly equal, but towards the end, the weight of fluid to that of the child, diminishes considerably, so that during the last weeks of pregnancy it scarcely equals a pound, and seldom more than eight ounces, whereas the medium weight of the child is usually between six and seven pounds: the quantity, however, varies considerably, sometimes amounting to several quarts. In the early months the absolute quantity increases, so that between the third and fourth months it sometimes equals as much as thirty-six ounces. Chemically it consists chiefly of water, a small quantity of albumen and gelatine, a peculiar acid called amniotic, with a little muriate of soda and ammonia, and a trace of phosphate of lime.
The source of the liquor amnii is still unknown. Dr. Burns asserts that "it is secreted from the inner surface of the membrane by pellucid vessels," but as he confesses that "these have never been injected or traced to their source (Principles of Midwifery, by J. Burns, M. D. p. 222.,) little weight can be attached to such a view." Meckel considers (Handbuch der Menschlichen Anatomie, vol. iv. p. 707,) that the greater part of it, especially in the early months, is a secretion from the maternal vessels, but that afterwards, as pregnancy advances, it becomes mingled with the excretions of the foetus. It appears to be a means of nourishment to the foetus during the first part of pregnancy, from the fact that it contains more nutritious matter in the early than in the latter months, since at that time a considerable coagulation is produced by alcohol, &c. The disappearance of this coagulable matter of the liquor amnii, towards the end of pregnancy, may be attributed to its having been absorbed at an earlier period, and to the process of nutrition being now carried on by other means. Besides being a source of nourishment to the foetus, it serves many useful purposes; it secures the foetus against external pressure or violence, and supports the regular distension of the uterus; on the other hand it diminishes and equalises the pressure of the foetus upon the uterus; during labour by distending the membranes into an elastic cone, it materially assists to dilate the os uteri; it also serves to lubricate and moisten the external passages.
Placenta. The placenta is formed essentially by the chorion and decidua; it is a flat, circular, or more or less oval mass, soft, but becoming firmer towards its edge. It is the most vascular part of the ovum, and by which it is connected most intimately with the uterus. Its longest diameter is generally about eight, its shortest about six inches; its greatest thickness is at that spot where the umbilical cord is inserted, which is usually about the middle of the placenta, although it occasionally varies considerably in this respect, the cord coming off sometimes at the edge. The placenta, as ordinarily seen after labour, is barely an inch in its thickest part, but when filled with blood or injection it swells very considerably, and is then little short of two inches. It is generally attached to the upper part of the uterus in the neighbourhood of one of the Fallopian tubes, and more frequently on the left side than on the right; its inner or foetal surface is smooth, being covered by the chorion, which at this part is much thicker.
The placenta cannot be distinguished from the other parts of the ovum until the end of the second month, at which period it covers nearly half the surface of the ovum, gradually diminishing in relative size, but increasing in thickness and absolute bulk up to the full period of utero-gestation. It forms a spongy vascular mass, its uterine surface being divided unequally into irregular lobes called cotyledons.
The uterine surface of a full-grown placenta is covered by a pulpy membrane, resembling in structure the decidua which covers the chorion, and of which it seems to be a continuation. This is always found present at the end of pregnancy: it covers the lobes of the uterine surface of the placenta, descending into the sulci which runs between them: in some parts it is thicker than in others, especially where it is connected with, or in fact becomes, the decidua of the chorion or decidua reflexa. This membrane, which has been called the placenta decidua, is pretty firmly attached to the vessels of the placenta, so as not to be separated without rupture; but by maceration, its texture is more or less destroyed, so that we may easily distinguish the extremities of these vessels. "This decidua, or uterine portion of the placenta," says Dr. Hunter, "is not a simple thin membrane expanded over the surface of the part: it produces a thousand irregular processes, which pervade the substance of the placenta as deep as the chorion or inner surface; and are every where so blended and entangled with the ramifications of the umbilical system, that no anatomist will perhaps be able to discover the nature of their union. While these two parts are combined, the placenta makes a pretty firm mass, no part of it is loose or floating; but when they are carefully separated, the umbilical system is evidently nothing but loose floating ramifications of the umbilical vessels, like that vascular portion of the chorion, which makes part of the placentula in a calf; and the uterine part is seen shooting out into innumerable floating processes and rugæ, with the most irregular and minutely subdivided cavities between them that can be conceived. This part answers to the uterine fungus in the quadrupeds: it receives no vessels demonstrable by the finest injection from those of the navel string; yet it is full of both large and small arteries and veins: these are all branches of the uterine vessels, and are readily filled by injecting the arteries and veins of the uterus, and they all break through in separating the placenta from the uterus, leaving corresponding orifices on the two parted surfaces." (Hunter, op. cit. p. 42.)
According to Lobstein's observations, although this membrane appears to be a continuation of the decidua which covers the chorion, it nevertheless does not exist during the earlier months. During the first months of pregnancy the placenta does not present a solid mass, with its uterine surface covered with projecting lobuli, as it does at the full term of pregnancy; but the vessels of which it is composed (foetal) are loose and floating, as if it had been subjected to maceration. It has been supposed, that this irregular lobulated appearance of the uterine surface of the placenta was produced at the moment of its separation from the uterus during labour; this, however, is not the case, for Lobstein having opened the uterus of a woman who died in the fifth month of pregnancy, and separated the placenta with great care, found these lobular prominences, although not yet covered by the membrane of which we have just spoken. Wrisberg, professor of anatomy at Göttingen, considered that this membrane was distinct from the decidua reflexa, since with care the two membranes can be easily separated.
In examining the uterine surface of a full grown placenta it is necessary to place it upon something convex, in order that it may resemble, as nearly as possible, the form which it had when attached to the concave surface of the uterus; the cotyledons are thus rendered prominent and separated from each other; the sulci, which run between them, are wide and gaping: whereas, when the placenta is laid upon a flat surface, its cotyledons are closely pressed together, and the sulci more or less completely concealed. On minute examination of these sulci a number of openings may be observed, varying in size and shape, but usually more or less oval, their edges distinct, smooth, and thin; on directing a strong light into some of the larger ones a number of smaller apertures may be observed opening into them, in much the same way as is observed when looking down a large vein. Some of these canals do not immediately lead to smaller orifices as above described, but open at once into an irregular-shaped cell or cavity, in the parietes of which numerous small apertures may be observed, through which blood oozes when the adjacent parts of the placenta are slightly pressed upon. Besides these openings at the bottom of the interlobular sulci, others may be seen here and there upon the cotyledons; these are generally smaller, their edges thicker, and in most instances they are round; but they are not so invariably met with as the openings between the cotyledons, these lobular projections being sometimes very thickly covered with placental decidua. The openings observed on the uterine surface of the placenta correspond to the mouths of the uterine veins and arteries, which, in the unimpregnated state, open into the cavity of the uterus, but which now, by means of the decidua, convey maternal blood to and from the placenta. "Any anatomist," says Dr. W. Hunter, "who has once seen and understood them, can readily discover them upon the surface of any fresh placenta; the veins, indeed, he will find have an indistinct appearance from their tenderness and frequent anastomoses, so as to look a good deal like irregular interstitial void spaces: the arteries which generally make a snake-like convolution or two, on the surface of the placenta, and give off no anastomosing branches, are more distinct." (Hunter, op. cit. p. 46.) From the observations of Messrs. Mayo and Stanley, and from their examination of the original preparations in the Hunterian museum at the College of Surgeons, London, illustrating this subject, it appears that, in all probability, most of the large thin-edged apertures at the bottom of the interlobular sulci are connected with the uterine veins; whereas, the smaller orifices, the margins of which are thicker, and which are chiefly observed upon the cotyledons, are continuations of the uterine arteries.
These openings were also pointed out by the late Dr. Hugh Ley, in describing the post mortem examination of a woman who had died at the full term undelivered (Med. Gaz. June 1, 1833:) "The uterine surface (of the placenta) thus detached from the uterus, exhibited its lobules with their intersecting sulci, even more distinctly than they are seen in the uninjected placenta; and in several parts there could be perceived, with the naked eye, small apertures of an oval form, with edges perfectly smooth, regularly defined, and thicker, as well as more opaque, than the contiguous parts which they penetrated." The communication between the openings of the placental cells, and the mouths of the uterine veins and arteries, which convey their blood to the placenta, as before observed, is effected by means of the placental decidua. The connecting portion of canal is of a flattened shape, runs obliquely between the uterus and placenta, and appears to be formed entirely of decidua. The manner in which the arteries pass to the placenta is very different to that of the veins: "the arteries," as Dr. W. Hunter observes, "are all much convoluted and serpentine; the larger, when injected, are almost of the size of crow-quills: the veins have frequent anastomoses." Mr. J. Hunter has described this point more minutely, and gives still more precise notions of the manner in which the arteries pass to the placenta. "The arteries of the uterus which are not immediately employed in conveying nourishment to it, go on towards the placenta, and, proceeding obliquely between it and the uterus, pass through the decidua without ramifying: just before they enter the placenta, making two or three close spiral turns upon themselves, they open at once into its spongy substance, without any diminution of size, and without passing beyond the surface as above described.
The intention of these spiral turns would appear to be that of diminishing the force of the circulation as it approaches the spongy substance of the placenta, and is a structure which must lessen the quick motion of the blood in a part where a quick motion of this fluid was not wanted. The size of these curling arteries at this termination is about that of a crow's quill. The veins of the uterus appropriated to bring back the blood from the placenta, commence from this spongy substance by such wide beginnings as are more than equal to the size of the veins themselves. These veins pass obliquely through the decidua to the uterus, enter its substance obliquely, and immediately communicate with the proper veins of the uterus; the area of those veins bear no proportion to their circumference, the veins being very much flattened."[21]
On examining these vessels in an injected uterus to which the placenta is attached, we shall therefore find that all traces of a regular canal or tube are suddenly lost upon their entering the placenta; each vessel (whether artery or vein) abruptly terminating in a spongy cellular tissue. If a blow-pipe be introduced into a piece of sponge, we shall have a very simple but correct illustration of the manner in which the uterine blood circulates through the placenta. The cell into which each vessel immediately opens is usually much larger than the rest, so that when the cellular structure of the placenta is filled with wax, a number of irregular nodules[22] are found continuous with these vessels and passing into an infinity of minute granules, which are merely so many casts of smaller cells. That this cellular tissue pervades the whole mass of the placenta, and communicates freely with the uterine vessels by which it is filled with blood, is proved by repeating a very simple experiment of Dr. Hunter, viz. "if a blow-pipe be thrust into the substance of the placenta any where, the air which is blown into the cellular part opens, and rushes out readily by, the open mouths both of the arteries and veins." (Hunter, op. cit. p. 46.) That it also envelopes the umbilical vessels of the cord is shown by the fact, that if a pipe be inserted beneath the outer covering of the cord near to its insertion into the placenta, we shall be able to "fill the whole placenta uniformly in its cellular part, and likewise all the venous system of the uterus and decidua, as readily and fully as if we had fixed the pipe in the spermatic or hypogastric vein; so ready a passage is there reciprocally between the cells of the placenta and the uterine vessels." (Ibid. p. 47.)
The maternal portion of the placenta therefore consists of a spongy cellular tissue, which is filled by the uterine vessels, and also of those trunks which pass through the decidua, and which form the communication between these vessels and the placental cells.
The foetal surface of the placenta is smooth and glossy, being covered by the amnion and chorion; it is much harder than the uterine surface, and is streaked over by the larger branches of the umbilical vein and arteries, which radiate irregularly from the point where the cord is inserted; and which pass beneath the amnion, and between the two layers of which the chorion is composed, to which they are intimately connected. These vessels supply the various lobuli of which the placenta is composed, so that each lobulus receives at least one of these branches; for, although the umbilical cord consists of two arteries and one vein, this arrangement does not continue into the body of the placenta. "Every branch of an artery," as Dr. Hunter observes, "is attended with a branch of a vein: these cling to one another, and frequently in the substance of the placenta entwine round one another, as in the navel string." (Ibid. p. 40.) Each cotyledon receives its own vessels, so that the vessels of one cotyledon have no direct communication with those of the adjacent ones, as proved by Wrisberg's examinations; for if we inject the vessel or vessels of one of these lobuli, the injection will not pass into those of the others. When the vessels have reached the cotyledons, they are divided and subdivided ad infinitum; they are connected together by a fine cellular membrane, which may be very easily removed by maceration, and then they may be seen ramifying in the most beautiful and delicate manner possible; the main branches having no communication or anastomosis with each other.
The umbilical arteries anastomose freely with each other upon the foetal surface of the placenta, before dividing into the branches above-mentioned; hence, if an injection be thrown into one umbilical artery it will return almost immediately by the other; but if this be tied also, the injection, after a time, will return by the umbilical vein, but not until all the vessels of the placenta have been filled, proving that there is a free passage of blood from the arteries into the veins.
From these remarks, founded chiefly on the admirable observations of the Hunters, and repeated examinations of the placenta, which we have made with the greatest care and impartiality, it may be stated with confidence, that the placenta consists of two portions--a maternal and a foetal. The maternal portion consists, as we have before observed, of a spongy cellular tissue; and also of those trunks which pass through the decidua, and which form the communication between the uterine vessels and the placental cells. The foetal part is formed by the ramifications of the umbilical vessels: "that each of those parts has its peculiar system of arteries and veins, and its peculiar circulation, receiving blood by its arteries, and returning it by its veins; that the circulation through these parts of the placenta differs in the following manner: in the umbilical portion the arteries terminate in the veins by a continuity of canal; whereas, in the uterine portion there are intermediate cells into which the arteries terminate, and from which the veins begin." (Hunter, op. cit. p. 48.)
Although various observations and anatomical injections show that to a certain degree, there is a communication between the uterus and the placenta, inasmuch as the blood of the former is received into the sinuses or cells of the latter, we possess no proof that the blood can pass from these sinuses into the umbilical vessels: on the contrary, every thing combines to prove that the circulation of the foetus is altogether independent of that of the mother. We know from daily experience that in labour at the full term of pregnancy, the placenta is easily expelled from the uterus: that, upon examining the surface which had been attached to the uterus we find no laceration, and that a discharge of more or less blood takes place for some days afterwards. We know, also, that when the placenta becomes detached from the uterus during the progress of gestation, it is followed by a considerable hemorrhage, which greatly endangers the life of the mother. These facts prove that there is a circulation of uterine blood in the placenta, which is destroyed upon its being separated from the uterus. That this uterine circulation in the placenta is unconnected with the circulation of foetal vessels in the placenta is proved by the fact first pointed out by Wrisberg, viz. that, where the mother has died from loss of blood, and the maternal vessels therefore drained of their contents, those of the foetus have been full of blood. Still farther to illustrate this fact, he killed several cows big with calf, by a large wound through the heart or great vessels, so as to ensure the most profuse and sudden loss of blood possible, and never found that the vessels of the calf were deprived of blood, although those of the mother were perfectly empty; moreover, no anatomist has ever yet succeeded in making injections pass from the foetal into the uterine vessels, or vice versâ. Lobstein has mentioned a mode of illustrating this fact (Essai sur la Nutrition du Foetus,) which is both simple and striking. Upon examining the uterine surface of a placenta which has been expelled at the full term, it presents the appearance of a spongy mass gorged with blood, which may be removed by washing or maceration, and if a placenta thus prepared be injected, the fluids will pass with the greatest facility from the umbilical arteries into the umbilical vein, but not one drop into its cellular structure; it is evident, therefore, that the blood which had filled the intervals between the vessels, and which had been removed by washing and maceration, could not have belonged to the foetus, but must have come from the mother; for if any of the vessels had been ruptured the injection would not have succeeded.
In concluding these observations upon the placenta, we may briefly state, that there is the same relation between the umbilical vessels and the maternal blood, which fills the placental cells, as there is between the branches of the pulmonary artery, and the air which fills the bronchial cell.[23]
Umbilical cord. The umbilical cord, funis, or navel string, is a vascular rope extending between the foetus and placenta, by which they are connected together. It usually arises, as we have before observed, from about the middle of the placenta, and terminates at the umbilical ring of the foetus; it consists of two umbilical arteries and one umbilical vein; the former conveying the blood from the common iliac arteries of the foetus to the cotyledons of the placenta; the latter formed by the union of the collected umbilical veins, on the inner surface of the placenta, and returning this blood to the foetus. In the early periods of pregnancy it also consists of the duct and vessels of the vesicula umbilicalis, the urachus, and more or less of the intestinal canal. The umbilical cord does not present the same form or appearance at every period of gestation; the younger the embryo, the shorter and thicker is the cord; in fact, there are no traces whatever of a cord at first, the embryo adhering, by its lower or caudal extremity, directly to the membranes. By the fifth or sixth week it becomes visible; at this early period the vessels of which it is composed pass from the foetus in a straight direction, but as pregnancy advances they become more or less spiral, winding round each other, and usually from left to right: according to Meckel, they take the opposite direction much less frequently, viz. in the proportion of one to nine.
The vessels of the umbilical cord are imbedded in a thick viscid substance; upon minute examination, it will be found to consist of a very fine cellular tissue, containing an albuminous matter which slowly exudes, when pressed between the fingers. This cellular tissue itself may be demonstrated by the inflation of air or injection with mercury: it seems to accompany the umbilical vessels as far as the posterior surface of the peritoneum; and Lobstein is of opinion that it is a continuation of the cellular tissue, which covers this membrane. (Lobstein, sur la Nutrition du Foetus. § 75.)
Externally, the umbilical cord is covered by a continuation of the amnion, which, although it be the inner membrane of the ovum, is the outer covering of the cord: in some places it is very thick and strong, and not easily ruptured. From repeated observations, the weakest part of the cord seems to be at about three or four inches distant from the umbilicus, this being the spot where it has invariably given way in every case we have seen, where the cord has been broken at the moment of the child's birth.
From the time of the commencement to the full time of utero-gestation, the cord becomes gradually longer, so that it attains an average length of from eighteen to twenty inches; this, however, varies remarkably. We have known the cord exceed forty inches; and a case is described by Baudelocque, where it was actually fifty-seven inches long: on the other hand, it is sometimes not more than four or five inches in length.
It is remarkable that the cord, which at the end of pregnancy is usually of about the same length as the foetus, is relatively much longer during the sixth month; hence we may conclude, that in those cases where knots have been found upon the cord, the knot must have been formed at this period when the foetus was small enough to pass through a coil of it.
Neither blood-vessels nor lymphatics have as yet been found in the structure of the cord itself. A filament of nerve from the solar plexus has been occasionally seen passing through the umbilical ring, and extending to a distance down the cord.
The vesicula umbilicalis and allantois, being essentially connected with the earliest grades of foetal development, will be considered under that head.
Embryo. There is, perhaps, no department of physiology which has been so remarkably enriched by recent discoveries, as that which relates to the primitive development of the ovum and its embryo. The researches of Baer, Rathke, Purkinje, Valentin, &c. in Germany; of Dutrochet, Prevost, Dumas, and Coste, &c. in France; and of Owen, Sharpey, Allen Thomson, Jones, and Martin Barry in England, but more especially those of the celebrated Baer, have greatly advanced our knowledge of these subjects, and led us deeply into those mysterious processes of Nature which relate to our first origin and formation.
These researches have all tended to establish one great law, connected with the early development of the human embryo, and that of other mammiferous animals, viz, that it at first possesses a structure and arrangement analogous to that of animals in a much lower scale of formation: this observation also applies of course to the ovum itself, since a variety of changes take place in it after impregnation, before a trace of the embryo can be detected.
At the earliest periods, the human ovum bears a perfect analogy to the eggs of fishes, amphibia, and birds; and it is only by carefully examining the changes produced by impregnation in the ova of these lower classes of animals, that we have been enabled to discover them in the mammalia and human subject.
As the bird's egg, from its size, best affords us the means of investigating these changes, and as in all essential respects they are the same in the human ovum, it will be necessary for us to lay before our readers a short account of its structure and contents, and also of the changes which they undergo, after impregnation. In doing this we shall merely confine ourselves to the description of what is applicable to the human ovum.
The egg is known to consist of two distinct parts, the vitellus or yelk surrounded by its albumen or white; to the former of these we now more particularly refer. The yelk is a granular albuminous fluid, contained in a granular membranous sac (the blastodermic membrane) which is covered by an investing membrane called the vitelline membrane or yelk-bag. The impregnated vitellus is retained in its capsule in the ovary, precisely as the ovum of the mammifera is in the Graafian vesicle. The whole ovary in this case has a clustered appearance, like a bunch of grapes, each capsule being suspended by a short pedicle of indusium.
In those ova which are considerably developed before impregnation, the granular blastermodic membrane is observed to be thicker, and the granules more aggregated at that part which corresponds to the pedicle, forming a slight elevation with a depression in its centre, like the cumulus in the proligerous disc of a Graafian vesicle. This little disc is the blastoderma, germinial membrane or cicatricula; in the central depression just mentioned is an exceedingly minute vesicle first noticed by Professor Purkinje of Breslau, and named after him: in more correct language it is the germinal vesicle.
According to Wagner, the germinal vesicle is not surrounded by a disc before impregnation; and it is only after this process that the above-mentioned disc of granules is formed. By the time the ovum is about to quit the ovary the vesicle itself has disappeared, so that an ovum has never been found in the oviduct containing a germinal vesicle, nothing remaining of it beyond the little depression in the cumulus of the cicatricula.
The rupture of the Purkinjean or germinal vesicle has been supposed by Mr. T. W. Jones to take place before impregnation; but the observations of Professor Valentin seem to lead to the inference that it is a result of that process, and must be therefore looked upon as one of the earliest changes which take place in the ovum or yelk-bag upon quitting the ovary.[24]
During its passing through the oviduct (what in mammalia is called the Fallopian tube,) the ovum receives a thick covering of albumen, and as it descends still farther along the canal the membrane of the shell is formed.
On examining the appearance of the ovum in mammiferous animals, and especially the human ovum, it will be found that it presents a form and structure very analogous to the ova just described, more especially those of birds. It is a minute spherical sac, filled with an albuminous fluid, lined with its blastodermic or germinal membrane, in which is seated the germinal vesicle or vesicle of Purkinje. When the ovum has quitted the ovary the germinal vesicle disappears, and on its entering the Fallopian tube it becomes covered with a gelatinous, or rather albuminous covering. This was inferred by Valentin, who considered that "the enormous swelling of the ova, and their passage through the Fallopian tubes," tended to prove the circumstance. (Edin. Med. and Surg. Journ. April, 1836.) It has since been demonstrated by Mr. T. W. Jones in a rabbit seven days after impregnation. The vitellary membrane seems, at this time, to give way, leaving the vitellus of the ovum merely covered by its spherical blastoderma, and encased by the layer of albuminous matter which surrounds it.
From what we have now stated, a close analogy will appear between the ova of the mammalia and those of the lower classes, more especially birds, which from their size afford us the best opportunities of investigating this difficult subject.
In birds, the covering of the vitellus is called yelk-bag; whereas, in mammalia and man it receives the name of vesicula umbilicalis. Its albuminous covering, which corresponds to the white and membrane of the shell in birds, is called chorion: by the time that the ovum has reached the uterus, this outer membrane has undergone a considerable change; it becomes covered with a complete down of little absorbing fibrillæ, which rapidly increase in size as development advances, until it presents that tufted vascular appearance, which we have already mentioned when describing this membrane.
The first or primitive trace of the embryo is in the cicatricula or germinal membrane, which contained the germinal vesicle before its disappearance. In the centre of this, upon its upper surface, may be discovered a small dark line;[25] "this line or primitive trace is swollen at one extremity, and is placed in the direction of the transverse axis of the egg."
As development advances, the cicatricula expands. "We are indebted to Pander,"[26] says Dr. Allen Thomson in his admirable essay above quoted, "for the important discovery, that towards the twelfth or fourteenth hour, in the hen's egg the germinal membrane becomes divided into two layers of granules, the serous and mucous layers of the cicatricula; and that the rudimentary trace of the embryo, which has at this time become evident, is placed in the substance of the upper-most or serous layer." "According to this observer, and according to Baer, the part of this layer which surrounds the primitive trace soon becomes thicker; and on examining this part with care, towards the eighteenth hour, we observe that a long furrow has been formed in it, in the bottom of which the primitive trace is situated; about the twentieth hour this furrow is converted into a canal open at both ends, by the junction of its margins (the plicæ primitivæ of Pander, the laminæ dorsales of Baer:) the canal soon becomes closed at the cephalic or swollen extremity of the primitive trace, at which part it is of a pyriform shape, being wider here than at any other part. According to Baer and Serres, some time after the canal begins to close, a semi-fluid matter is deposited in it, which on its acquiring greater consistence, becomes the rudiment of the spinal cord; the pyriform extremity or head is soon after this seen to be partially subdivided into three vesicles, which being also filled with a semi-fluid matter, gives rise to the rudimentary state of the encephalon." "As the formation of the spinal canal proceeds, the parts of the serous layer which surrounds it, especially towards the head, become thicker and more solid, and before the twenty-fourth hour we observe on each side of this canal four or five small round opaque bodies, these bodies indicate the first formation of the dorsal vertebræ.
"About the same time, or from the twentieth to the twenty-fourth hour, the inner layer of the germinal membrane undergoes a farther division, and by a peculiar change is converted into the vascular mucous layers." (A. Thomson, op. cit.) It will thus be seen, that the germinal membrane is that part of the ovum in which the first changes produced by impregnation are observed. The rudiments of the osseous and nervous systems are formed by the outer or serous layers; the outer covering of the foetus or integuments, including the amnois, are also furnished by it. "The layer next in order has been called vascular, because in it the development of the principal parts of the vascular system appears to take place. The third, called the mucous layer, situated next the substance of the yelk, is generally in intimate connexion with the vascular layer, and it is to the changes which these combined layers undergo, that the intestinal, the respiratory, and probably also the glandular systems owe their origin." (A. Thomson, op. cit. p. 298.)
The embryo is therefore formed in the layers of the germinal membrane, and becomes, as it were, spread out upon the surface of the ovum: the changes which the ovum of mammalia undergoes appear from actual observation, to be precisely analogous to those in the inferior animals. (Baer, Prevost and Dumas.) From the primitive trace, which was at first merely a line crossing the cicatricula, and which now begins rapidly to exhibit the characters of the spinal column, the parietes of the head and trunk gradually approach farther and farther towards the anterior surface of the abdomen and head until they unite; in this way the sides of the jaws close in the median line of the face, occasionally leaving the union incomplete, and thus appearing to produce in some cases the congenital defects of hare-lip and cleft palate. In some way the ribs meet at the sternum; and it may be supposed that sometimes this bone is left deficient, and thus may become one of the causes of those rare cases of malformation, where the child has been born with the heart external to the parietes of the thorax. In like manner the parietes of the abdomen and pelvis close in the linea alba and symphysis pubis, occasionally leaving the integuments of the navel deficient, or, in other words, producing congenital umbilical hernia, or at the pubes a non-union of its symphysis with a species of inversion of the bladder, the anterior wall of that viscus being nearly or entirely wanting.
The cavity of the abdomen is therefore at first open to the vesicula umbilicalis or yelk, but this changes as the abdominal parietes begin to close in; in man and the mammalia merely a part of it, as above mentioned, forms the intestinal canal, whereas, in oviparous animals the whole of the yelk-bag enters the abdominal cavity, and serves for an early nutriment to the young animal. Another change connected with the serous or outer layer of the germinal membrane is the formation of the amnion. The foetal rudiment which from its shape has been called carina, now begins to be enveloped by a membrane of exceeding tenuity, forming a double covering upon it; the one which immediately invests the foetus is considered to form the future epidermis; the other, or outer fold, forms a loose sac around it, containing the liquor amnii. Whilst these changes are taking place in the serous layer of the germinal membrane, and whilst the intestinal canal, &c. are forming on the anterior surface of the embryo, which is turned towards the ovum, by means of the inner or mucous layer, equally important changes are now observed in the middle or vascular layer. "In forming this fold," says Dr. A. Thomson, "the mucous layer is reflected farthest inwards; the serous layer advances least, and the space between them, occupied by the vascular layer, is filled up by a dilated part of this layer, the rudiment of the heart." (Op. cit. p. 301.)
Whilst this rudimentary trace of the vascular system is making its appearance, minute vessels are seen ramifying over the vesicula umbilicalis, forming, according to Baer's observations, a reticular anastomosis, which unites into two vessels the vasa omphalo-meseraica. (British and Foreign Med. Rev. No. 1.) These may be demonstrated with great ease in the chick: the cicatricula increases in extent; it becomes vascular, and at length forms a heart-shaped net-work of delicate vessels, which unite into two trunks, terminating one on each side of the abdomen.
The umbilical vesicle now begins to separate itself more and more from the abdomen of the foetus, merely a duct of communication passing to that portion of it which forms the intestinal canal. The first rudiment of the cord will be found at this separation; its foetal extremity remains for a long time funnel-shaped, containing, besides a portion of intestine, the duct of the vesicula umbilicalis, the vasa omphalo-meseraica (the future vena portæ,) the umbilical vein from the collected venous radicles of the chorion, and the early trace of the umbilical arteries. These last-named vessels ramify on a delicate membranous sac of an elongated form which rises from the inferior or caudal extremity of the embryo, viz. the allantois; whether this is formed by a portion of the mucous layer of the germinal vesicle, in common with the other abdominal viscera, appears to be still uncertain: in birds this may be very easily demonstrated as a vascular vesicle, arising from the extremity of the intestinal canal; and in mammalia, connected with the bladder by means of a canal called urachus: from its sausage-like shape, it has received the name of allantois.
The existence of an allantois in the human embryo has been long inferred from the presence of a ligamentous cord extending from the fundus of the bladder to the umbilicus, like the urachus in animals. But from the extreme delicacy of the allantois, and from its function ceasing at a very early period, it had defied all research, until lately when it has been satisfactorily demonstrated in the human embryo by Baer and Rathke. It occupies the space between the chorion and amnion, and gives rise occasionally to a collection of fluid between these membranes, familiarly known by the name of the liquor amnii spurius, which, strictly speaking is the liquor allantoidis.
The function of the allantois is still in a great measure unknown. In animals it evidently acts as a species of receptaculum urinæ during the latter periods of gestation; but it is very doubtful if this be its use during the earlier periods. It does not seem directly connected with the process of nutrition, which at this time is proceeding so rapidly, first by means of the albuminous contents of the vitellus, or vesicula umbilicalis, and afterwards by the absorbing radicles of the chorion; but, from analogy with the structure of the lower classes of animals, it would appear that it is intended to produce certain changes in the rudimentary circulation of the embryo, similar to those which, at a later period of pregnancy, are effected by means of the placenta, and after birth by the lungs, constituting the great functions of respiration.
In many of the lower classes of animals, respiration (or at least the functions analogous to it) is performed by organs situated at the inferior or caudal extremity of the animal: thus for instance, certain insect tribes, as in hymenoptera, or insects with a sting, as wasps, bees, &c.; in diptera, or insects with two wings, as the common fly; and also the spider tribe, have their respiratory organs situated in the lower part of the abdomen. In some of the crustacea, as, for instance, the shrimp, the organs of respiration lie under the tail between the fins, and floating loosely in the water. Again, some of the molusca, viz. the cuttle-fish, have the respiratory organs in the abdomen. We also know that many animals, during the first periods of their lives, respire by a different set of organs to what they do in the adult state: the most familiar illustration of this is the frog, which, during its tadpole state, lives entirely in the water.
As the growth of the embryo advances, other organs whose function is as temporary as that of the allantois, make their appearance: these also correspond to the respiratory organs of a lower class of animals, although higher than those to which we have just alluded,--we mean bronchial processes or gills. It is to Professor Rathke (Acta Naturæ Curios. vol. xiv,) that we are indebted for pointing out the interesting fact, that several transverse slit-like apertures may be detected on each side the neck of the embryo, at a very early stage of development. In the chick, in which he first observed it, it takes place about the fourth day of incubation: at this period the neck is remarkably thick, and contains a cavity which communicates inferiorly with the oesophagus and stomach, and opens externally on each side by means of the above-mentioned apertures, precisely as is observed in fishes, more especially the shark tribe; these apertures are separated from each other by lobular septa, of exceedingly soft and delicate structure. Rathke observed the same structure in the embryo of the pig and other mammalia; and Baer has since shown it distinctly in the human embryo. It is curious to see how the vascular system corresponds to the grade of development then present: the heart is single, consisting of one auricle and one ventricle; the aorta gives off four delicate, but perfectly simple branches, two of which go to the right, and two to the left side; each of these little arteries passes to one of the lobules or septa at the side of the neck, which correspond to gills, and having again united with the three others, close to what is the first rudiment of the vertebral column, they form a single trunk which afterwards becomes the abdominal aorta. In a short time these slit-like openings begin to close; the bronchial processes or septa become obliterated, and indistinguishable from the adjacent parts; the heart loses the form of a single heart; a crescentic fold begins to mark the future division into two ventricles, and gradually extends until the septum between them is completed. It is also continued along the bulb of the aorta, dividing it into two trunks, the aorta proper and pulmonary artery; at the upper part the division is left incomplete, so that there is an opening from one vessel to the other, which forms the ductus arteriosus.[27] A similar process takes place in the auricles, the foramen ovale being apparently formed in the same manner as the ductus arteriosus; these changes commence in the human embryo about the fourth week, and are completed about the seventh.
At first the body of the embryo has a more elongated form than afterwards, and the part which is first developed is the trunk, at the upper extremity of which a small prominence less thick than the middle part, and separated from the rest of the body by an indentation, distinguishes the head. There are as yet no traces whatever of extremities, or of any other prominent parts; it is straight, or nearly so, the posterior surface slightly convex, the anterior slightly concave, and rests with its inferior extremity directly upon the membranes, or by means of an extremely short umbilical cord.
The head now increases considerably in proportion to the rest of the body, so much so, that at the beginning of the second month, it equals nearly half the size of the whole body: previous to, and after this period, it is usually smaller. The body of the embryo becomes considerably curved, both at its upper as well as its lower extremity, although the trunk itself still continues straight. The head joins the body at a right angle, so that the part of it which corresponds to the chin is fixed directly upon the upper part of the breast; nor can any traces of neck be discerned, until nearly the end of the second month.
The inferior extremity of the vertical column, which at first resembles the rudiment of a tail becomes shorter towards the middle of the third month, and takes a curviture forwards under the rectum, in the fifth week the extremities become visible, the upper usually somewhat sooner than the lower, in the form of small blunt prominences. The upper close under the head, the lower near the caudal extremity of the vertebral column. Both are turned somewhat outwards, on account of the size of the abdomen; the upper are usually directed somewhat downwards, the lower ones somewhat upwards.
The vesicula umbilicalis may still be distinguished in the second month as a small vesicle, not larger than a pea, near the insertion of the cord, at the navel, and external to the amnion. From the trunk, which is almost entirely occupied by the abdominal cavity, arises a short thick umbilical cord, in which some of the convolutions of the intestines may still be traced. Besides these it usually contains, as already observed, the two umbilical arteries and the umbilical vein, the urachus, the vasa omphalo-meseraica, or vein and artery of the vesicula umbilicalis, and perhaps, even at this period, the duct of communication between the intestinal canal and vesicula umbilicalis, the foetal extremity of which, according to Professor Oken's views, forms the processus vermiformis.
The hands seem to be fixed to the shoulders without arms, and the feet to adhere to the ossa illi; the liver seems to fill the whole abdomen; the ossa innominata, the ribs, and scapulæ are cartilaginous.
In a short time the little stump-like prominences of the extremities become longer, and are now divided into two parts, the superior into the hand and the fore arm, the inferior into the foot and leg; in one or two weeks later, the arms and thighs are visible. These parts of the extremities which are formed later than the others, are at first smaller, but as they are gradually developed they become larger. When the limbs begin to separate into an upper and lower part, their extremities become rounder and broader, and divided into the fingers and toes, which at first are disproportionately thick, and until the end of the third month are connected by a membranous substance analogous to the webbed feet of water birds; this membrane gradually disappears, beginning at the extremities of the fingers and toes, and continuing the division up to their insertion. The external parts of generation, the nose, ears, and mouth appear after the development of the extremities. The insertion of the umbilical cord changes its situation to a certain degree; instead of being nearly at the inferior extremity of the foetus as at first, it is now situated higher up on the anterior surface of the abdomen. The comparative distance between the umbilicus and pubis continues to increase, not only to the full period of gestation, when it occupies the middle point of the length of the child's body, as pointed out by Chaussier, but even to the age of puberty, from the relative size of the liver becoming smaller.
Though the head appears large at first, and for a long time continues so, yet its contents are tardy in their development, and until the sixth month the parietes of the skull are in great measure membranous or cartilaginous. Ossification commences in the base of the cranium, and the bones under the scalp are those in which this process is last completed.
The contents of the scull are at first gelatinous, and no distinct traces of the natural structure of the brain can be identified until the close of the second month; even then it requires to have been sometimes previously immersed in alcohol to harden its texture. There are many parts of it not properly developed until the seventh month. In the medulla spinalis no fibres can be distinguished until the fourth month. The thalami nervorum opticorum, the corpora striata, and tubercula quadrigemina, are seen in the second month; in the third, the lateral and longitudinal sinuses can be traced, and contain blood. In the fifth we can distinguish the corpus callosum; but the cerebral mass has yet acquired very little solidity, for until the sixth month it is almost semi-fluid. (Campbell's System of Midwifery.)
About the end of the third, during the fourth, and the beginning of the fifth months, the mother begins to be sensible of the movements of the foetus. These motions are felt sooner or later, according to the bulk of the child, the size and shape of the pelvis, and the quantity of fluid contained in the amnion, the waters being in larger proportionate quantity the younger the foetus.
The secretion of bile, like that of the fat, seems to begin towards the middle of pregnancy, and tinges the meconium, a mucous secretion of the intestinal tube which had hitherto been colourless, of a yellow colour. Shortly after this the hair begins to grow, and the nails are formed about the sixth or seventh month. A very delicate membrane (membrana pupillaris,) by which the pupil has been hitherto closed, now ruptures, and the pupil becomes visible. The kidneys, which at first were composed of numerous glandular lobules (seventeen or eighteen in number,) now unite, and form a separate viscus on each side of the spine; sometimes they unite into one large mass, an intermediate portion extending across the spine, forming the horse-shoe kidney.
Lastly, the testes, which at first were placed on each of the lumbar vertebræ, near the origin of the spermatic vessels, now descend along the iliac vessels towards the inguinal rings, directed by a cellular cord, which Hunter has called Gubernaculum testis: they then pass through the openings carrying before them that portion of the peritoneum which is to form their tunica vaginalis.
The length of a full-grown foetus is generally about eighteen or nineteen inches; its weight between six and seven pounds. The different parts are well developed and rounded; the body is generally covered with the vernix caseosa;[28] the nails are horny, and project beyond the tips of the fingers, which is not the case with the toes; the head has attained its proper size and hardness; the ears have the firmness of cartilage; the scrotum is rugous, not peculiarly red, and usually containing the testes. In female children the nymphæ are generally covered entirely by the labia, the breasts project, and in both sexes frequently contain a milky fluid. As soon as a child is born, which has been carried the full time, it usually cries loudly, opens its eyes, and moves its arms and legs briskly; it soon passes urine and fæces, and greedily takes the nipple. (Naegelé's Hebammenbuch.)
Thus, then, in the space of forty weeks, or ten lunar months, from an inappreciable point, the foetus attains a medium length of about eighteen or nineteen inches, and a medium weight of between six and seven pounds. As these observations on the development of the ovum show that the structural arrangement of the embryo undergoes a succession of changes, by which it gradually rises from the lowest to the highest scale of formation, so we shall find it furnished with a succession of means for its nutrition, each corresponding more or less to the particular grade of development which it may have attained. Its earliest source of nourishment is doubtless the vitellus, or albuminous contents of the vesicula umbilicalis. The radicle or primitive trace, in this respect, bears a strong analogy to the seed of a plant; it brings with it its own supply of nourishment for its first stage of growth; in the latter, the cotyledons afford nourishment to the little plumula, until, by the formation of roots and absorption of moisture from the surrounding soil, it is enabled to support the early rudiment of the future plant. The early function of the chorion is very analogous to that of roots; it is an absorbing apparatus, collecting nourishment by means of its numerous absorbing fibrillæ: hence, according to Lobstein, the umbilical vein exists for some time previous to the umbilical arteries, and seems to perform an office in the foetus similar to that of the thoracic duct at a later period; its radicles or absorbing extremities seem to absorb a milky fluid, which after the first two months is found in the placenta, and which must be looked upon as a means of nourishment which does not exist in the latter months. This milky fluid was noticed by Leroux, who even then expressed his doubts, whether the radicles of the umbilical vein receive blood from the mother, or whether they only serve to absorb a white fluid which resembles chyle. In some manuscript notes of Dr. Young's lectures, which were taken by the late Dr. Parry, of Bath, when a student at Edinburgh, we find the following observation: "There is evidently in the placenta, besides blood-vessels, some other substance, which serves to absorb juices from the uterus, and to convert these into a chylous matter proper to nourish the foetus, and this matter is absorbed by the umbilical veins. This seems to be proved from the consideration of the placenta of animals which have cotyledons; for, on squeezing these glandular substances, we force out a sort of chylous liquor, and these are surrounded by the placenta, which absorb their liquor and convey it to the foetus."
The absorbing power of the umbilical vein continues till the fifth month; during the second or third, the foetus receives a good deal of nourishment from the liquor amnii, which at this period contains a considerable quantity of albuminous matter; this diminishes in the latter months of pregnancy. Moreover the body of the foetus begins to be covered with the vernix caseosa towards the seventh month, so that in the eighth and ninth months the absorption of liquor amnii by the skin is considerably impeded.
How far the full formed placenta, as seen after the fifth month, serves as a means of nutrition to the foetus, may still be a matter of doubt; its chief use after this period is, as we have already shown, for the purpose of producing certain changes in the blood of the foetus analogous to those of respiration;[29] still, however, it would seem that its function of nutrition is not entirely at an end, even at a late period of pregnancy. The numerous little granules of phosphate of lime, which are frequently found on the uterine surface of a full-grown placenta at a time when ossification is rapidly advancing in the foetal skeleton, would surely lead us to infer that the placenta in some way or other supplies the materials for this process.
Foetal circulation. We have already shown, that, in the early stages of development, the heart of the embryo is single, consisting of one auricle and one ventricle; that a septum gradually divides these into two parts until the double heart is formed, leaving two openings of communication between the right and left sides, the one between the auricles called the foramen ovale, the other between the pulmonary artery and aorta, viz. the ductus arteriosus.
From these and other peculiarities it will be seen that the foetal circulation differs essentially from that of a child after birth; and, in order to comprehend the nature and mechanism of the changes which take place in it when respiration first commences, it will be necessary that these peculiarities should be thoroughly understood. The condition of the foetus must also be remembered: surrounded by the liquor amnii, the foetus does not respire; its lungs have as yet been unemployed; they are therefore small and collapsed, and present a firm solid mass, nearly resembling liver in appearance. In this state but little blood from the pulmonary arteries can circulate through them; for, as the extreme ramifications of these vessels are distributed upon the mucous membrane lining the bronchi and air-cells, the free passage of blood through them will in great measure depend upon a previous condition of the air-cells. The pulmonary arteries in the foetal state are therefore small, and transmit but a small quantity of blood into their numerous ramifications, just sufficient to keep pervious these vessels which after birth are to be so greatly distended: in this state the lungs when thrown into water sink.
Hence, as the pulmonary arteries do not afford a sufficiently free exit to the contents of the right side of the foetal heart, nature has provided it with a peculiar means for carrying off the overplus quantity of blood, which is poured into the right auricle from the vena cava. This is attained first by the foramen ovale, an oval-shaped opening in the septum between the right and left auricles, and furnished with a semilunar valvular flap, so constructed, as to allow a free passage for the blood from the right to the left auricle, but none in the contrary direction. By this means a considerable quantity of blood is transmitted at once from the right to the left auricle, and, consequently, much less into the right ventricle and pulmonary artery. Still, however, more blood passes into the right ventricle than the pulmonary artery, in the collapsed state of the foetal lungs, is capable of conveying away. The pulmonary artery is therefore continued beyond its bifurcation into the aorta at its curvature, by means of the ductus arteriosus, which, in the full-grown foetus, forms a short thick passage between these two vessels; and in this manner is the right ventricle enabled to get rid of its surplus quantity of blood. Thus we see that the foetal heart although consisting of two auricles and two ventricles, continues to perform the functions only of a single heart, both ventricles assisting simultaneously to propel the same column of blood, viz. that of the aorta, and thus enabling the heart to act with considerable power.
The chief part of the blood, which flows through the iliac arteries, instead of being sent to the inferior extremities, is carried into the umbilical arteries, which passing up along the sides of the bladder meet the umbilical vein at the navel, and thus form the vessels of the umbilical cord. These arteries convey the blood of the foetus to the placenta, where, having undergone changes to which we have already alluded, it is returned by the umbilical vein. This vessel, which afterwards forms the round ligament of the liver, passes through the umbilicus along the anterior edge of the suspensory ligament; it supplies the left lobe with blood, and having given off a communicating branch to the vena portæ, which supplies the right lobe, it passes at once by a short passage, called canalis venosus, into the vena cava.
Thus, then, the peculiarities of the foetal circulation may be considered as four, viz. the foramen ovale, or passage from the right to the left auricle; the ductus arteriosus, or communication from the bifurcation of the pulmonary artery into the arch of the aorta; the umbilical arteries arising from the iliac arteries, and carrying the blood along the cord into the placenta; and, lastly, the canalis venosus, or passage between the umbilical vein and vena cava.
Let us now examine the changes which take place in the foetal circulation at the moment of the child's birth. The child, which had hitherto been immersed in the bland and warm medium of the liquor amnii, is at once exposed to the action of the external air. By means of the sympathy existing between the skin and respiratory muscles, sudden and convulsive efforts at inspiration take place; the air-cells of the lungs become partially inflated, and, after a short time as the respiration increases in power and activity, become distended throughout their whole extent. The thorax rises; the flaccid diaphragm, which hitherto had been pushed up by the large foetal liver, now contracts, pressing down the liver into its natural situation. The lungs, from being a hard solid heavy substance, resembling liver, at once become inflated, elastic, and crepitous, light and permeable to air in every part.
The capillary terminations of the pulmonary artery, which ramify in the mucous membrane, forming the parietes of the air-cells, and which hitherto had been firmly compressed by the collapsed state of the foetal lungs, are suddenly rendered pervious throughout their whole extent. By this means, a vacuum, as it were, is formed in the ramifications of the pulmonary artery; each inspiration is accompanied by a rush of blood from the right ventricle into the newly-inflated structure. The pulmonary artery, at its bifurcation, swells and becomes turgid: the blood is carried off into its numerous ramifications as fast as the right ventricle can supply it; this may be easily understood from the law, in anatomy, viz. that the area of two arteries is greater than that of the trunk from which they bifurcate. From this state of distension, the distance between the pulmonary artery and the aorta is increased; the ductus arteriosus, which has now become empty, is stretched, and thus partially closed; the right auricle, which, but for the foramen ovale, could not have cleared itself of the whole quantity of blood which was poured into it from the vena cava, is now enabled to transmit its entire contents into the right ventricle; the left auricle, which before birth was supplied only by the foramen ovale from the right auricle, is now rapidly filled by the blood brought into it by the four pulmonary veins;--the equilibrium between the two auricles becomes altered;--the right, which hitherto had been somewhat gorged with blood, is now able to clear itself with facility; whereas, the left, which was but partially supplied, is now distended with a much greater quantity: there is now rather a disposition for the blood to regurgitate from the left to the right auricle; this, however, is prevented by the semilunar fold of the foramen ovale, which now acts as a valve, and generally becomes firmly attached to the septum. The obliteration of the canalis venosus at the posterior margin of the liver, and of the umbilical vein at the anterior edge, may, we think, be explained by the changes which necessarily follow the inflation of the lungs: the diaphragm, when it contracts, pulls down the liver into its natural situation; the distance, therefore, between the liver and the heart is increased, and the canalis venosus is consequently stretched, and considerably pressed upon, and precisely the same results follow with the umbilical vein.