Hearing and how to keep it

Front matter

AMERICAN HEALTH PRIMERS.

Edited by W. W. KEEN, M.D.,

Fellow of the College of Physicians of Philadelphia; Surgeon to St. Mary's Hospital, etc.

Chapter II

Physics and Physiology of Sound and Hearing. 41 Physics and Physiology of Sound . , . .41 Physiology of Hearing 43

VI CONTENTS.

PART 11.

gifeoitraua of i\zxx Improper freatuuni CHAPTER I.

PAGE

CHAPTER 11.

Diseases of the Middle Ear . . . -77

CHAPTER I. CHAPTER n

The Care of the Ear in Disease, including the Relief of Partial Deafness and the Education of Partially Deaf Children and Deaf-Mutes 131

Diagram of the entire Auditory Apparatus of Man ; Dimensions nearly natural.

The front part of the Auditory Canal, the front half of the Drum-Head, and part of the Eustachian Tube are supposed to be removed.

I. The side of the temple-bone cut through. 2. Outer surface of temple. 3. Upper wall of bony part of hearing canal. 4. Ligament holding hammer-bone to roof of drum-cavity. 5. Roof and upper part of drum-cavity. 6. Semicircular canals. 7. Anvil bone. 8. Hammer-bone. 9. Stirrup-bone. 10. Cochlea, or "snail-shell." 11. Drum-head cut across, and looked at sideways. 12. Isthmus of Eustachian tube. 13. Mouth of Eustachian tube, in the throat. 14. The hearing, or auditory, canal. 15. Lower wall of bony canal of hearing. 16. Lower wall of cartilaginous part of canal, at its junction with the bony part. 17. Wax-glands. 18. Lobule. 19. Upper wall of cartilaginous part of hearing canal. 20. The mouth of the auditory canal. 21. The anti-tragus.

viii

HEARING,

AND

HOW TO KEEP IT.

PART I. Anatomy and Physiology of the Ear

CHAPTER I.

STRUCTURE OF THE EAR.

THE ear is the most complicated organ of special sense. Its most important parts lie deeply hidden in the hardest bone in the body, the petrous bone, and on this account its complex nature is rendered all the more difficult to study. The external ear, /. e, the auricle, or ear of common language, and the auditory canal which leads to the drum-head, the drum-head itself, and parts of the drum-cavity or tympanum are visible from without, and easily accessible in the living ; but all other parts of the ear are not naturally visible. Furthermore, the dimensions of the various lO HEARING, AND HOW TO KEEP IT.

parts of the organ of hearing, excepting the outside appendage, the auricle, are very small, and in the case of the inner ear, where the nerve of hearing is spread out, they are microscopic. At the outset, therefore, the anatomical knowledge requisite to understanding the functions of the ear is hard to get. Although it is proposed in this little book to speak chiefly of the function of the ear and how to preserve it, and also to show what should not be done in many cases of injury and disease of the ear, nevertheless, the entire subject will be more clearly understood, and it is hoped, more profitable, if the anatomy and some of the more important diseases of the ear are alluded to. Hence, at the beginning, we shall briefly sketch the anatomy and physiology of the entire hearing apparatus in man.

The exter7ial ear comprises the auricle, that part usually called the ear, the auditory canal, and the membrana tympani, or drum-head. The drum-head is really the partition between the external ear and the middle ear or drum-cavity, and partakes in the structures of each of these portions of the ear, as will be shown further on.

The middle ear, or drum proper — the tympanum — lies, as its name would indicate, between the external ear and the internal ear, or labyrinth.

For the present, it will be sufficient to bear in mind that the middle ear is an air-cavity, and hence a

STRUCTURE OF THE EAR. II

characteristic of warm-blooded animals, or of those whg live on land. It comprises the Eustachian tube, which connects it with the upper back part of the throat, and the mastoid portion of the temporal bone, parts yet to be more minutely described. The middle ear contains the smallest bones in the human body, the so-called auditory ossicles, viz., the hammer, the anvil, and the stirrup, thus named simply from their resemblance in shape to these implements.

Through this important cavity, the middle ear, pass two nerves, one, the facial, on its way to the face, and the other, really a branch of the facial, the so-called cord of the drum (the chorda tympani), on its way to the tongue. A closer analysis of this cavity will be given, when its anatomy claims our special attention.

The internal ear is often called the labyrinth, on account of its perplexing structure and the obscurity which has hung about its composition and function, and which still hangs about some parts of it, so that it still deserves its name. It comprises the vestibule, an anterior part, as implied in its name, and the cochlea, or snail-shell, lying in front of the vestibule, the semicircular canals which lie behind it, and the auditory nerve, or nerve of hearing, lying beyond, between it and the brain, which sends nerve -branches to it.

This short statement will serve as a definition of the three grand divisions of the organ of hearing.

HEARING, AND HOW TO KEEP IT.

It must be borne in mind that all these parts of the ear lie very near the brain, in the temporal or petrous bone, and hence their ailments are readily communicated to the central organ of the nervous system. The petrous bone, the hardest, most rock-like bone

Fig. I.— The Auricle.

1, The pit of the anti-helix; 2, 6, 10, The so-called helix, the curved edge of the auricle; 3, The meatus, or mouth of the auditor^^ canal; 4, The tragus ; 5, The lobule ; 7, The anti-helix ; 8, The concha ; 9, The anti-tragus.

in the frame, demands consideration, not only because it contains the ear, but also because it is an important key in the architecture of the skull, being part of the base and side of the skull, and hence helping in the protection of the brain.

The External Ear. — The auricle, or ear of common language, is a shell of cartilage, covered with skin, closely fitting every groove and ridge of the underlying cartilaginous frame, excepting at its lowest pendant part. Here the skin is reflected over a cushion of delicate fat, making the lobule, that part to which ear-rings are usually fastened. In some cases the cartilage of the auricle dips into this cushion of fat, and when the lobule is pierced, preparatory to wearing ornaments, the cartilage is wounded, and a very painful inflammation is set up. The auricle is well supplied with blood-vessels, nerves, and lymphatics, being firmly held in place to the side of the head by ligaments, which, however, permit of a certain degree of passive mobility in man. The auricle gradually passes into the auditory canal, very much as the mouth of a trumpet fades into the tube of the instrument. The skin of the auricle, which is really part of the skin of the face, is extended into the external auditory canal, the next inner-lying part of the ear, and continues down this passage to and over the drum-head ; though, of course, in the latter structure, it becomes extremely web-like and transparent.

The auricle is abundantly supplied with the little glands characteristic of the skin, viz., the sebaceous and the sweat glands. The former secrete a natural lubricator for the skin, but are not of much importance, in this respect, in the auricle. They are most numerous in that part of the auricle called the concha, its deepest part, just at the entrance to the auditory canal (Frontispiece, 17). The entire surface of the auricle is covered with downy hairs, which, however, attain a very luxuriant and stiff growth at that part called the tragus, or goat (Fig. L, 4). This, doubtless, like the beard, is a protection.

The sweat glands of the auricle are most numerous on the hinder surface, an important consideration in the management of the ears of infants, for, if their auricles are pressed constantly against the head, as is too likely to be the case, softening and chafing of these parts must be inevitable.

The auricle is therefore a highly organized part of the hearing apparatus, as well as of the face and head.

Physiogno77iy, — The artist studies the auricle with the contours of the head and face. Praxiteles, by making the top of the auricle pointed instead of curved, in a celebrated statue, has handed down through the ages a sculpture we call his Faun. In modern literature, a hint at a similar form has been wonderfully utilized by the genius of Hawthorne, in the weird character of Donatello. In so far as the Faun of Praxiteles or the Donatello of Hawthorne were inhuman, the shape of the auricle alone has been employed to demonstrate it in the former, and to imply it, and to excuse crime in the latter. A popular feeling is, that a small and well-shaped ear in man is not only a beauty, but a sign of good breeding ; while, on the other hand, a large, prominent auricle is a sign of vulgarity. Giotto, in his drawing of Envy, in the chapel of the Arena, at Padua, represents the auricle as superhuman in size. The position of the auricle may be a national peculiarity, as in the Egyptians, in whom the auricles are placed high in the head. Considerable interest has been aroused respecting the meaning of a little point or prominent fold very often found at the upper posterior edge of the auricle in man. Both artist and anatomist have been attracted to these prominences, which have been found in the ears not only of men, but of monkeys. Advocates of the theory of the descent of man from the monkey, thought they had found in this little blunt point on the auricle another reason for their belief; but these defects in the auricle have been shown by Ludwig Mayer, of Germany, to be the results of inflammation before birth, and therefore they are congenital. They are in fact remnants of the edge of the cartilage of the auricle, the greater portion of which has been eroded by disease, as above stated.

The Auditory Canal, — The auditory canal may be said to be a continuation inward of the trumpet, of which the auricle is the broad and flaring mouth

(Frontispiece, 14). The auditory canal is a passage one inch and a quarter long, averaging one- quarter of an inch in diameter, slightly narrower at its central part than at either end. It is composed one-third of cartilage and two-thirds of bone, and is lined throughout with skin, a continuation of that of the auricle, already considered. A general idea of its nature can be gained by consulting the Frontispiece. It is closed hermetically at its inner end by the drum-head, or membrana tympani. The skin of the auditory canal, besides the usual elements of skin, viz., sebaceous, perspiratory, and hair glands, contains at its outer part, around its entire calibre, the ceruminous, or ear-wax glands. These are between one and two thousand in number, and resemble in their structure the sweat-glands ; they are indeed what the anatomist calls modified sweat-glands. Their function is to secrete the wax of the ear, with which all are familiar. This substance is of the highest importance to the comfort and health of the auditory canal. So long as the outer end of the canal wall is smeared with this wax, the skin is free from itching, and the ear is comfortable. Its peculiarly glutinous and bitter nature is a protection against the incursion of insects, and it also prevents the growth of fungi, or mould, in the canal.

The Drum-Head^ or the Memh'ana Tympani, — The drum-head, or rnembrana tympanic is that part

STRUCTURE OF THE EAR.

of the ear forming the partition between the external ear and the middle ear, or drum-cavity. The

Fig. II. — Outer Surface of the Drum- Head. Magnified about y/2, times. 1

1, The flaccid part of the drum-head ; 2, Short process ; 3, The back fold of the drum-head ; 4, The anvil's long and descending limb shining through from behind the drum-membrane ; 5, The true membrane ; 6 and 10, Inner end of bony canal forming frame for drum-head ; 7, The pyramid of light ; 8, Lower part of the hammer ; 9, The front fold of the drum-head.

drum-head is popularly called the drum ; but this is not a strictly correct term to apply to it. It is really the outer wall of the drum. The latter name is applicable only to the cavity of the drum or middle ear.

The drum-head is almost circular, about a quarter of an inch in diameter, and o-io mm., or about ^4-^ in., in thickness, /. e. about as thin as fine gold-beaters' skin. It is composed of three distinct layers: i. An outer one, of skin, a continuation of that lining the auditory canal ; 2. A middle layer of fibrous tissue, the thickest of the three, and that on which the otiier layers are stretched ; 3. The inner layer is of mucous membrane, continuous with the mucous membrane lining the cavity of the drum. It is thus seen that the drum-head partakes of the structure of the external and of the middle ear. Running from above, downward and backward, in the central line of the drum-head, there is an opaque, white ridge. This is the first evidence we get by inspection of the chain of auditory bonelets connecting the drum-head with the drum-cavity, and finally with the internal ear, where the nerve lies. (Fig. II., 2-8.) This is the so-called handle of the hammer, one of the bonelets alluded to. This handle is firmly attached to the middle layer of the drum-head, and is thus all the more likely to move to and fro with every motion of the drum-head. The further advantage of this intimate connection between the hammer-handle and the drum-head will be shown when considering the mechanism of the auditory bones as a whole. The drum-head is situated at the bottom of the external auditory canal, in a bony ring of its own, and is therefore about an inch and a quarter from the mouth of the auditory canal at the auricle.

When the healthy drum-head is viewed in its proper position, there are several features which at once attract attention. It is nearly circular in shape ; it is of a delicate pearl or bluish color, excepting along the ridge marking the position of the handle of the hammer-bone, where it is decidedly whiter and opaque. It will also at once be noticed that the drum-head looks like a thin membrane stretched over a dark, or nearly dark, cavity. Such indeed is the case, for the only light in the drum-cavity beyond, is transmitted to it through the translucent drum-head.

The surface of the drum-head is seen to be not only very smooth, but polished and lustrous. So marked is its lustre at the lower and front part, between the tip of the ridge, alluded to as the handle of the hammer, and the circumference of the drum-head, that at this point, owing to the concavity of the membrane and its position in the axis of the auditory canal, a bright, cone-shaped reflection of light is seen running in one of the diameters of the membranes. (Fig. II., 7.) This has been called the ^'cone of light," and should be found in ears which have a drum-head of normal position and lustre.

The handle of the hammer alluded to above, is more prominent at its upper part than anywhere else on the drum-head. This prominence has been named

HEARING, AND HOW TO KEEP IT.

the short process, and plays a conspicuous part in the plotting out of the membrane by anatomists. (Fig. II., 2.) It looks not unlike the head of a pimple.

Fig. III.— Inner Surface of Drum-Head of Man. Magnified about 3j^ times.

, Short limb of anvil, attached to back part of outer bony wall of tympan'c cavity; 2, Body of anvil-bone; 3, Head of hammer-bone; 4, Neck ot hammer; 5 -11, Chorda tympani nerve This marks also the boundary line of the pockets and folds of drum-head. The latter are shown in Fig. 2, at 9 and 3. 6, Front part of drum-membrane ; 7-8, Bony frame around drum-head; 9, The lower part of handle of hammer-bone; 10, Lower part of long limb of anvil-bone. To the point 10, the head of the stirrup is attached.

From it, backward and forward, to the circumference, pass two prominent ridges, or folds in the membrane. (Fig. II., 3 and 9.) These are called the folds of the drum-head, and serve as the upper boundary of the membrane proper. There is a part of the membrane above them, which contains no fibrous tissue, like the middle layer of the drum-head proper, and to this part the name of the flaccid membrane is given. (Fig. II., I.) Directly behind lies the neck and head of the hammer ; never visible, however, in health.

The line of these folds is nearly the line of support for the leverage exercised by the hammer bonelet. The handle is the lower arm of this lever, and the neck and head of the hammer, the part not visible from without (see Fig. III., 3 and 4), is the upper arm. The axial line is an important part in the function of the entire chain of bonelets, yet to be described. A general idea of the topography of the drum-head, as marked out by these parts just alluded to, is gained by consulting Figs. II. and III.

The Middle Ear. — We have now come to the consideration of the anatomy of the middle ear, the seat of most of the diseases of the organ of hearing. As has been stated, page 11, the middle ear is composed of the drum-cavity and its important adjuncts — the Eustachian tube and the mastoid cells. Of these three parts, the drum-cavity is the most delicate and complicated in structure, and most liable to^sease.

We shall therefore give our first attention to its structure and functions.

Drum- Cavity. — For the sake of .convenience and accuracy, the drum-cavity may be said to be enclosed by four walls, a roof, and a floor. The four walls are named the front, the back, the inner, and the outer. Its most important contents are the three auditory ossicles, or the small bones of the ear. This cavity is about half an inch in height and width, and from the twelfth to the sixth of an inch deep, measuring from within outward, and lies of course just behind the drum-head. It is lined with mucous membrane, a continuation of that of the nose, throat, and Eustachian tube, which is reflected over the contents of the cavity. This is the drum proper, and the only part of the ear to which the term drum or tympanum should be applied. But great confusion constantly arises from applying the name ^^drum " to the drum-head, or the membrana tympani.

Auditory Bonelets. — The auditory bonelets, or ossicles, as they are more usually called, are three in number: The hammer, or malleus ; the anvil, ox incus ; and the stirrup, or stapes, named from their resemblance in shape to these implements. They form the so-called '^chain of bones" of the ear. In passing into the drum from without, the first little bone one comes to is the hammer, which is the largest of the three.

STRUCTURE OF THE EAR.

It is divided into a head, neck, and handle. It

is about a quarter of an _. ___ o-u .i. t^

^ Fig. IV. — The three Bones of

inch long; the handle Hearing of the right ear in their forms about half of this natural position, seen from withlength, and the head is in. Magnified about 4 times, about the one-eighth of an inch thick. Its general appearance and various parts, magnified, about four times, may be learned from Fig. IV.

It is the handle of this small bone which is inserted into the drum-head, and holds, as it were, the latter taut. (Fig. II., 8, 2.)

The hammer, besides this attachment to the drum-head, is held in position by ligaments which fasten it to the roof and the outer wall of the drum-cavity.

Next in order, passing inward, comes the anvil. This small bone is divided into a body and two processes or limbs — a long and a short one. (Fig. IV., 4, 5.) The former is called also the descending limb, while the shorter one is sometimes called the horizontal limb. It, too, like the hammer, is held to the upper and posterior wall of the tympanic cavity by liga-

:, Head of hammer ; 2, is above the long process and to the left of short process of the hammer ; 3, The handle of the hammer ; 4,The long limb of the anvil ; 5, Its short limb ; 6, The stirrup.

HEARING, AND HOW TO KEEP IT.

ments. This bone is a trifle smaller than the hammer, to which it is joined as seen in Fig. IV. This

Fig. V. —The Bones of Hearing. Magnified 4 times. A B C

Head;

Neck ; 3, Short process ; 3-4, Handle ;

A. Right hammer. 5, The long process.

B. Right ailvil. i. Body ; 2, Joint surface for union with hammer (see Fig. IV.) ; 3, Long process or leg. The point 3 unites with the head of the stirrup ; 4, Short process or leg, which is joined to the back part of the tympanic wall at i, Fig. III.

C. Right stirrup, i, Head; 2 and 4, The legs; 3, The foot-plate, which fits into the oval window.

joint has the peculiarity of unlocking, if the handle of the hammer is pulled outward ; but if the handle of the hammer is pushed inward, this joint is only more firmly locked, and the hammer carries the anvil with it. This will be seen to be important in the mechanism of the ossicles as conductors of sound vibrations inward to the inrjer ear.

The action of this joint has been likened to some watch-keys which wind the watch when turned in a certain direction, but when turned in the opposite way, the handle is unlocked from the barrel, and the watch remains unwound.

The innermost of the three ossicles is the stirrup, the smallest bone in the human body, its entire length being one-eighth of an inch. It is divided into a head, a neck, two legs, and a foot-plate. The head is a cup-shaped button, at the junction of the two legs, and is designed to receive a knob-like projection on the end of the anvil's long limb. (Fig. V., C, i.) The two limbs of the stirrup are furrowed on the inner surface, which makes them lighter, but does not take from their strength. The foot-plate (Fig. IV., 6) is ovoid in shape, and fits accurately into the oval window of the labyrinth, where it is hermetically held by a fibrous packing. Thus, the connection between the outer ear and the drum-head, and the labyrinth and the nerve of hearing, is completed. It may aid the understanding to liken this chain of bones to a bridge, v/hich thus connects the drum-head with the labyrinth and the auditory nerve.

This entire bridge, or chain of bones, moves as a whole in and out. It is this kind of oscillation, to and fro, on the part of the drum-head and the chain 3

HEARING, AND HOW TO KEEP IT.

of the Roof.

tween 3 and 4 times. (Helm-

holtz.

13 12 of auditory bones, that causes the foot-plate of the stirrup to play backward and forward with minutest Fig. VI. -View of the Left excursions, and it is this Tympanum,or Drum-Cavity, movement of the footfrom above, after removal plate that sets the water Magnified be- ^^ ^^^^ labyrinth into vibrations, which in turn impress the auditory nerve, and produce hearing.

Boundaries of the Drum.

— The roof of the drum-cavity is the boundary between the brain and the drum. This partition

nerve, marking also the boundary of jg y^j-y );\-{iXi^ SOmCtimCS it

the so-called pouches of the drum ;

3, Front ligament of the hammer; 4, haS chiuks iu it; hcUCe

ternal ligament of support of the

hammer; 7, Attachment of the short cavity is liable tO paSS

limb of the anvil to the drum-cavity; jnto the braiu and prove

8, Ligament of support for latter; 9,

Body of anvil-bone ; 10, The stirrup iat3-i.

muscle ; 11, The head of the stirrup- L^j- ^\^^ rCadcr UOW im-

restof bone invisible from this point;

12, Joint between anvil and ham- aginc a right drum-cavity

mer; 13, Head of hammer; 14, The opeUcd bcfore him, by stretcher muscle of the drum, run- i r • c

ning from the Eustachian tube across ^^^ rCmOVal of itS rOOf. the drum-cavity to the hammer. ^\^^ aUtCrior Or frOUt

wall, /. e, the wall nearest the throat, is chiefly remarkable for the orifice connecting it with the Eusta-

1, Entrance to Eustachian tube and the throat; 2 and 6, The chorda tympani chian tube (Fig. VI. i), called the tympanic, or drummouth of the Eustachian tube. There is also on its upper and inner part a little pyramidal elevation (Fig. VI. 14), through which plays the thread-like tendon of the muscle called the tensor tympani, the stretcher of the drum. This muscle is a delicate offshoot from the muscles of the palate, which work the Eustachian tube.

When these muscles, in passing up from the palate, have nearly reached the bony portion of the tube, /. e, the beginning of the tympanic cavity, they stop, but send on to the drum-cavity a small and slender muscle. This muscle, a little over an inch long, lies in a narrow bony canal of its own, on the upper part of the bony portion of the Eustachian tube, until it reaches the drum-cavity. Here the tympanic end of this delicate bony canal is narrowed and extended free into the cavity of the drum, forming the aforesaid pyramidal elevation. Through this, as a fulcrum, the tendon of the '^stretcher of the drum " {tensor tympani) passes, nearly at a right angle, to the drum-head, where it is inserted into the back part of the neck of the hammer bonelet. (Fig. III., near line 5.) It can now be understood how any contraction in the delicate muscle just named, can be communicated to the hammer-bone, and by it to the drum-head.

The back wall, like the front, is narrow. In its upper part is the opening which connects the drum-

HEARING, AND HOW TO KEEP IT.

Fig. VII. — View of Inner Surface of Temporal Bone, and of the Inner Surface of Drum-Head, also of the Eustachian Tube and Mastoid Cells in Section. Natural Size. (Politzer.)

I, 2, and 14, Inner surface of the temple ; 3, Head cf hammer-bone ; 4, The tensor tympani, or stretcher-muscle of the drum ; 5, Mouth of Eustachian tube, in throat; 6, The narrow isthmus of the tube, and, 7, its opening into the drum-cavity ; 8, Drum-head ; 9, 10, Mastoid cells ; 11, Handle of hammer ; 12, Anvil-bone ; 13, Short limb of latter, attached to outer bony wall of drum-cavity. This also marks entrance to mastoid cells, 9, 10.

cavity with the mastoid cells. (Fig. VI., 8, also Fig. VII., 13.)

It is thus shown how the drum-cavity communicates, in front, with the Eustachian tube and throat, and behind with the mastoid cells, and it can also be seen that air conveyed by the Eustachian tube to the drum-cavity is also conveyed to the mastoid cells.

Wider and more intricate in their topography are the outer and inner tympanic walls.

The outer wall of the drum-cavity is composed mainly of the drum-head. The bony ring in which the drum-head is stretched, forms the limit of the outer wall. In close connection with this wall, /. e. the drum-head, is the handle of the hammer and the chorda tympani nerve. (Fig. III., 9 and 5.) There are also on the upper and inner part of this outer wall certain folds of the mucous membrane, around the chorda tympani nerve, called the pouches of the drum-head. That fold in front of the hammer, between it and the circumference of the drum-head, is called the anterior pouch, (Fig. II., 9;) the fold behind the hammer is the posterior fold or pouch, and is the larger of the two. (Fig. II., 3.)

The inner v^2^\. demands close examination in order to understand its divisions. On this wall is a convexity, called the promontory, which is caused by the outward projection of the lower turn of the cochlea, yet to be described. (Fig. VIII., 5.) This eminenqe 3"'"

HEARING, AND HOW TO KEEP IT.

is usually seen through the drum-head, as a paleyellowish spot. Here the inner and outer walls are

Fig. VIII. -Inner Wall of Drum- ^^^'^'^ . ^^g^^her, Cavity: left side. Magnified twice. ^^^ ^^ ^^"^^^ ^^^^^"^ (Henle.) tdich Other. Just

above the promontory is the oval window, (Fig. VIII., 4,) which receives the foot ' plate of the stirrup, and behind and below the promontory is the round window.

From the head of the stirrup runs the stirrup-muscle.

, Facial nerve entering its canal; 2, Tendon of stretcher of the drum cut across ; 3, Eustachian tube; 4, The stirrup-bone; 5, The promontory; 6, The stirrup-musde; 7, The (Fig. VIII., 6.) canal in which the facial nerve runs,