Normal histology : a manual for students and practitioners

Front matter

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Med e

NORMAL HISTOLOGY.

Chapter I. The Cells

Histology is that medical science which treats of the microscopic normal anatomy of tissues of the human body.

The various tissues of the body are constructed, primarily, of cells and intercellular substance.

Histology first treats of the cell as a tissue-element and later discusses the relation of the various tissues to each other as found in the different organs of the human body.

The Typical Cell. — The cell is typically a minute mass of protoplasm, irregular iu shape, and having embedded in its substance a spherical body, the nucleus. Each cell has a structure and individuality peculiar to itself, and is divided into cell- wall, cell-body, nucleus, nucleolus, and centrosome.

The cell-body^ or cytoplasm, constitutes the larger portion of the cell and is divided into the spongloplasMy a reticulum of delicate fibres; the hyaloplasm, which is a clear semifluid substance filling the spaces between the fibres ; and lastly the metapdasm, which consists of the small granules often found in the cell-protoplasm.

The nucleus is a round body within the cell and composed of the nuclear membrane or wall, and the nuclear matrix, a semifluid fibrillated or reticulated substance. The nuclear fibrils are of two varieties, the chromatin and the achromatin fibrils, respectively, according to whether they stain readily or not.

A small highly refractive body is often found within the meshwork of the nucleus, called the nucleolus. There may be one or several nuclei present in a nucleus.

2— Ilis.

THE CELLS.

The eentrosome is a small refractive body within the nucleus, concerned in the multiplication of the cell. During this pr oeess it leaves the nucleus and appears in the cytoplasm or cell-body. It is surrounded by a clear area with delicate radiating filaments.

Specialized Cells. — Certain cells have peculiar charaeteris-

Fig. 1.

Schematic diagram of a cell: a, ectoplasm, composed of hyaloplasm ; h, spongioplasm; c, chromosome, composed of “chromatin,” and forming a part of the intranuclear reticulum ; between these chromatic fibres is the achromatin ; d, hyaloplasm in the meshes of the spongioplasm ; c, one of the two nucleoli represented in the diagram ;/, one of eight bodies constituting the metaplasm represented ; g, eentrosome, with radiate arrangement of the surrounding spongioplasm ; h, nuclear membrane. (Dunham.)

ties, as those with ezYia, or hair-like processes, and those with long proto})lasmic arms, as in nerve-cell fibres.

Cells are classified also according to form, function, motion, irritability, and methods of reproduction.

Reproduction of Cells. — Cells multiply by direct division or

REPRODUCTION OF CELLS.

Fig. 2.— Continuous convolution. Fig. 3.— Equatorial or aster stage.

Fig. 6.— Diaster stage. Fig. 7.— Double segmented convolution.

Diagrammatic representation of stages of karyokinesis. (Flemming.)

THE CELLS.

b lidding j and indirect division or hai'yohinesiSy mitosis or haryo- 7n it os is.

Direct Division. — In this process of reproduction a constriction appears in the centre of tlie cell and it separates into two parts. This method is the less frequent, and seems often to result from abnormal processes, in which the division of the nucleus is not accompanied by a division of the cell, thus forming multi nucleated cells — e. g.^ giant cells.

Direct division may occur along with indirect division in many leucocytes, decidual cells, cartilage-cells, and epithelial cells of the bladder.

Indirect Division. — This is the usual method and involves a series of complicated changes in the nucleus. If the process be reduced to a tabular enumeration of its stages, they will be the following :

a. liesting Nucleus. — The centrosome enlarges, passes out into the cytoplasm, and divides into two attraction-spheres. T1 le nucleus also enlarges and the chromatin-fibrils form a dense convolution, called the close skein.

b. Close Skein. — The chromatin-fibrils now become thicker, less convoluted, and arrange themselves into loops, called the loose skeins.

c. Loose Skein. — The fibrils now form in loops or chromosomes and with the attraction-spheres make the spindle.

d. 31othe7'-Star. — The loops are now arranged as a wreath with each apex toward the centre of the cell, resembling a star.

e. Diaster. — Each looj) undergoes longitudinal cleavage, splitting into halves, and the two separate wreaths or daughterstars are drawn ajiart by the attraction-spheres to the extreme opposite poles of the cell.

/. Division of the Cell. — A constriction now appears in the cell-wall and a division into halves occurs completely.

g. Neiv Nuclei. — Each daughter-wreath undergoes the reverse cycle of changes, and the nuclei of the new cells are formed as in the first cell before division.

The Ovum. — The first cell from which all cells or tissues are formed is the ovum, and by multiplication of this cell and

THE OVUM.

of the resulting daughter-cells three primary layers originate, namely, the ectoderm^ the mesoderm^ and the entoderm.

Spindle, showing chromosomes, asters, and centrosomes.

Showing four stages of nucleus.

The normal tissues are classified into four groups — the epithelial, the connective, the muscxdar, and the nervous tissue.

Resting nucleus and loose skein.

Cell, showing four asters.

Karyokinesis— indirect division of the cell.

All the tissues of the body are derived from these three blastodermic layers, as follow :

THE CELLS.

I. From the ectoderm —

The e})itheliiim of the outer surface of the body, hair, nails, etc. ;

The epithelium of the nasal tract ;

The epithelium of the mouth ;

The enamel of the teeth ;

The tissues of the nervous system ;

The retina and the crystalline lens.

II. From the mesoderm —

The connective tissues, including areolar, tendon, cartilage, bone, and dentine ;

The muscular tissues (except the muscles of the sweat-glands) ;

The tissues of the vascular and lymphatic systems, including their endothelium and circidating cells;

The sexual glands and passages (exee])t the vagina) ;

The kidneys and ureters (except the bladder and urethra).

1 1 r. From the entoderm —

The epithelium of the digestive tract (except the mouth and anus) ;

The epithelium of the respiratory tract ;

The e})ithelium of the urinary bladder and urethra ;

The epithelium of the thyroid and thymus bodies.

QUESTIONS.

What is histology?

Of what are the tissues constructed ?

Define a cell.

Name the parts of a cell.

What is the cell-wall?

What is the cell-body ?

Define a nucleus.

What is the nucleolus?

What is a centrosome?

How do cells reproduce?

Describe direct division.

What are the other names for indirect division ? ^ ^

Wliat ])art of the cell is principally concerned in indirect cell-division? Name the stages of indirect cell-division.

From wdiat do all cells originate ?

Name the three primary layers.

How do we divide ti.ssues?

What tissues are derived from the ectoderm? What from the mesoderm? What from the entoderm ?

THE EPITHELIAL TISSUES.

C II A P T E R II.

THE EPITHELIAL TISSUES.

Origin. — The epithelial tissues are derived from the ectoderm and entoderm, except the epithelium of the kidneys, ureters, and sexual glands, which are from the mesoderm.

Composition. — Epithelium is composed largely of cells separated by a small amount of intercellular substance holding them together.

Epithelium contains no bloodvessels, but obtains its nutrition by absorption of the nutritive juices conveyed by means of the little spaces or clefts within the cement-substance between the cells.

The nerve-supply of epithelium is not abundant, and the existence of nerve-fibrils within the epithelium in many places has not been established, but in other localities of extreme sensibility, as the tactile surfaces, nerve-fibrils terminating among the epithelial cells have been demonstrated.

Occurrence. — The epithelial cells cover the skin, the mucous aud serous cavities, and enter into the formation of the glands.

Types of Cell. — Epithelial cells are divided :

a. According to form, as columnar, cuboidal, polyhedral, spheroidal, tessellated (pavement), and scaly;

h. According to function, as glandular (mucous, peptic, oxyntic, etc.), serous, and sensory.

Cells may be ciliated, flagellated, or have amoeboid processes.

Types of Tissue. — Epithelial tissues are classified according to the number of layers of cells and the character of the superficial layer, as follows :

I. Squamous — (a) simple (single-layer) and (Ih) stratified (several layers).

II. Columnar — (a) simple (single-layer) and [h) stratified (several layers).

III. Modified — (a) ciliated, {h) goblet, (c) pigmented.

IV. Specialized — (a) glandular, ih) neuro-epithelium.

THE EPITHELIAL TISSUES.

I. Squamous Epithelium :

a. Simple (single-layer). — This type consists of a single layer of thin, flattened cells with a large nucleus, and is found lining the air-sacs of the lung and in a few other places.

b. Stratified (many-layer). — This is more common and is arranged in several layers. The shape and size of the cells vary in the diflerent layers ; those in the deeper layers are cuboidal or spheroidal, while those on the surface are flattened like scales. This variety is widely distributed, and found in stratified sqiiammis epithelium, oesophaprus of rabbit : a, deeper layers of rounded germinal cells; b, more superficial layers of flattened cells ; c, surface layer of horny cells ; d, underlying fibrous tissue ; e, papillary projection from the fibrous layer. (Dunham.)

the epidermis of the skin, the mouth, etc. That lining the bladder and ureter is sometimes called epithelium.

II. Columnar Epithelium :

a. Simple (single-layer). — This is of a single layer of elongated, more or less cylindrical or hexahedral cells, perjiendicular to a basement-membrane, and found in the intestines, in certain portions of the kidney, etc.

h. Stratified (many-layer). — In this type, occasionally the outer — i. e.y most sujierfleial — cells are distinctly columnar, while in the deeper layers they are irregular. It occurs in the trachea, olfactory mucous membrane, larger gland-ducts, etc.

MODIFIED EPITHELIUM.

III. Modified Epithelium :

a. Ciliated. — Tliis variety is limited to the most superficial layer of columnar cells, if stratified, and consists of delicate, hair-like processes on the outer end or free surface of the cell. These cilia are modifications of the eell-proto])lasm, and when carefully studied by special methods of staining are found to be made up of an outer layer of hair-like processes, next a cuticular layer, with a row of basal e/ramdes immediately below this, and lastly a series of fine threads converging tow^ard the nucleus of the cell. These last make up the fibrillar structure of the protoplasm. It occurs principally in the respiratory tract, w here the cilia are supposed to

Ciliated columnar epithelium (stratified) from trachea, showing ciliary wave.

(Nichols and Vale.)

remove small particles of dust by keeping up a vibration or sweep centrifugally toward the nose.

b. Goblet. — Between the columnar cells of the most superficial layer of columnar epithelium, if stratified, lining mucous surfaces, are found elliptical cells resembling goblets, and containing mucus, which is discharged upon the outer surface of the epithelium. These cells are sometimes called unicellular f/lands, or gland-cells. They are distinguished from the other cells by their larger size and clear protoplasm. This type occurs in all mucous membranes, especially in the intestinal tract.

c. Pigmerded. — When epithelial cells eontain a coloring-

THE EPITHELIAL TISSUES.

matter, as in the deeper layers of the epidermis of certain races and the outer layer of the retina, this variety is present.

Simple columnar epithelium and goblet-cells, from the intestine. Shows the striated free cuticular margin of the cells in this situation. (Nichols and Vale.)

IV. Specialized Epithelium :

a. Glandular. — This is found lining the glands, and the cells are columnar, spherical, or polyhedral in shape. The protoplasm often shows special changes indicating the character of the secretion.

Endothelium on a serous surface of the frog : a, stoma bounded by endothelial cells with granular cytoplasm ; h, pseudostoma. The nuclei of the cells are not represented. (Klein.)

h. N euro- Epithelium. — This is a type of cells modified so as to aid the nerves, which terminate in or near them, to appreciate the special senses, and are found in the retina, nose, etc.

THE CONNECTIVE TISSUES.

THE ENDOTHELIAL TISSUES.

Origin. — Endothelial tissues are developed from the mesoderm.

Classification. — This variety of tissue is usually classified with the epithelial tissues on account of its resemblance especially to the squamous, but more properly belongs to the connective tissues, as it owes its origin to the same layer of the blastoderm.

Composition. — It consists of a single layer of very thin polygonal flat cells having faintly granular protoplasm and a flattened oval nucleus. The small amount of intercellular cement-substance, and the slightly wavy borders of the cells cause their boundaries to appear indistinct unless special methods of staining are resorted to. Small openings, called stomata^ occur between the cells and allow the cavities lined with these cells, to communicate with the lymph- vessels.

These stomata are made up of a single layer of cubical cells with granular protoplasm.

Endothelium forms the lining of serous cavities, lymphand blood-vessels. In the latter places the cells are of an irregular oblong shape, with serrated borders.

THE CONNECTIVE TISSUES.

Origin. — These tissues are all developed from the mesoblastic layer of the blastoderm, and by specialization and differentiation of the intercellular substance are formed the various types of this group.

Composition. — Connective tissues are composed of cells separated by much intercellular substance or fibres, and may be solid, gelatinous, or fluid. As the name implies, these tissues hold together the other tissues and thus supply the framework of the body.

Classification. — They are divided into three main groups —

I. Fibrous connective tissues.

II. Cartilage.

III. Bone.

Fibrous connective tissues are subdivided into — (A) the chief

THE CONNECTIVE TISSUES.

Fibres of white fibrous tissue teased apart to show the individual fibrils. (Duuham.)

varieties: (a) white fibrous, (6) yellow elastic, and (c) areolar; into — (B) the special varieties : (a) gelatinous, (b) adenoid, and (c) adipose.

Elastic fibres. From subcutaneous areolar tissue. (Schafer.)

FIBROUS CONNECTIVE TISSUES, а. Mliite fibrous is composed of layers or bundles of fine silky fibrils, parallel or interlacing. This tissue is found most typical in tendons, and the cells are arranged in long chains between the fibres. Two kinds of cells are noted in this tissue, the fixed or stellate and the wandering, which resemble the leucocytes.

б. Yellow elastic occurs as a network of branching yellow

Areolar pssue. I reparation from the subcutaneous tissue of a young rabbit: c , enaotnelioid cell ; p p, cells with granular cytoplasm ; c, c,f, cells of the fusiform or stellate variety not yet fully developed ; the white fibres are in bundles pursuing a wavy course ; the elastic fibres are delicate and form a very open network ; g, leucocyte oi a coarsely granular variety. (Schafer.)

fibres, nearly the same width throughout their length, and when broken curled at the ends. This tissue occurs in the ligamentum nuchte and helps to make up areolar tissue.

c. Areolar is widely distributed and occurs in the subcutaneous, subserous, and submucous tissues. It is composed of both white fibrous and yellow clastic, which interlace to form a network in which are embedded connective-tissue corpuscles or cells.

THE CONNECTIVE TISSUES.

The density of areolar tissue depends upon whether the bundles of fibres are numerous, making a very compact interlacement, or whether they form a loose, open network, lietween the meshes of fibres is a semifiuid clear substance known as the matrix, or ground-substance.

Gelatinous or mucous tissue is found in the jelly of Wharton of the umbilical cord and the vitreous humor of the eye.

Embryonic connective tissue (mesenchym- Adipose tissue. Crystals of fatty atons tissuel : a, nucleus of stellate cell ; acids are represented in two of the b, cytoplasmic process. The intercellular sub- cells. (Nichols and Vale.) stance is of gelatinous consistency and optically homogeneous. (Bohm and bavidoff.)

It consists of large stellate cells embedded in a soft substance through which are scattered a few fibres and wandering cells.

This tissue is really not a separate variety, but should be considereid only as an early stage of developing fibrillar connective tissue.

In the mucous tissue of the vitreous humor of the eye are less cells and the semifluid ground-substance is very abundant

CARTILAUK.

Adenoid or lymphatic, tissue makes up the stroma of the lymphatic glaiuls, aiul sometimes called retiform.

This tissue is a delicate network of minute fibrils and contains lymplioid cells within its meshes.

Adipose or fatty tissue is widely distributed and consists of spherical connective-tissue cells, distended with oil derived from its protoplasm. The nucleus and remaining cell-body have been pushed to one side and appear crescent-sha])ed, while the oil is surrounded by the thin cell-wall. This tissue is held together by a delicate areolar tissue.

QUESTIONS.

What are the cliaracteristics of epithelium ?

Where are epithelial tissues found?

How do we divide the cells?

Give a classification according to the shape of the cell ; according to the function.

How are epithelial tissues classified ? Name the four principal varieties. What is simi>le scpiamous epithelium? Stratified epithelium?

What is simple columnar epithelium? Stratified epithelium?

Describe ciliated epithelium. Where is it found?

Describe goblet-cells.

Where are pigmented cells found ?

Describe glandular epithelium.

Where do we find neuro-epithelium?

What is endothelium, and where is it found ?

From what two layers are most epithelial tissues derived?

What are the exceptions?

What are connective tissues?

What are the characteristics of connective tissues ?

Name the three groups of connective tissues.

Describe white fibrous ; yellow elastic ; areolar.

Where do we find gelatinous tissue? Where adenoid tissue?

Describe adipose tissue?

Chapter III. Cartilage

Cartilage is a variety of connective tissue consisting of cells or corpuscles embedded in a condensed intercellular substance or matrix, the character of which gives rise to three tvpes : the hyaline, i\\o fibrous, and the elastic.

CARTILAGE.

This tissue represents a transition between the connective tissues and bone, and is distinguished from the fibrous eonnective tissues by the hard and dense consistency of its matrix and the shape of its cells.

Hyaline Cartilage. — This consists of a clear, nearly homogeneous matrix j with very delicate fibres holding together its glassy substance. The cells are large, irregular, and oval in shape, have large nuclei, and are grouped in patches. They lie in small spaces called lacuim, and the matrix around the cells appears condensed, making a capsule.

Hyaline cartilage. (Nichols and Vale.)

The cells in the superficial layers are more flattened, smaller, and spindle-shaped than those in the deeper layers, and on the outer surface the cells are arranged in parallel rows.

The outer covering of the cartilage is called the 'perichondrium^ and consists of dense fibrous tissue.

Hyaline cartilage is found in the articular ends of bones, ribs, trachea, etc.

Fibrous cartilage is hyaline cartilage to which have been added bundles of Avhite fibrous connective tissue throughout its matrix to give increased strength and flexibility. The cells of this variety are less numerous, and are generally

ELASTIC CARTILAGE.

arranged in small groups. It is not so widely distributed, and is found in the intervertebral disks.

Firj. 22.

Fibrocartilage. Section from human intervertebral disk. The cell to the left presents a branching process extending into the intercellular substance. (Schafer.)

Elastic cartilage differs from the preceding varieties in that it contains yellow elastic fibres in the matrix to give it great elasticity.

This type is found in the ears, epiglottis, etc.

Elastic cartilage; section from human external ear; a, cartilage-cell ; b, c, network of elastic fibres in the intercellular substance. (Buhm and Davidoff’ ) iiis.

BONE.

BONE.

Bone is a type of connective tissue, dense in structure, composed of cells or corpuscles and a matrix impregnated with lime salts.

Bone, like all the other connective tissues, possesses a large amount of intercellular substance, but differs from these in that it has a deposit of lime salts within the interfascicular cement-substance, and to this deposition is its hard and dense nature due. When we remove the lime salts (clecalcification) from bone and only the organic framework remains, the

Fig. 24

Ground section of dried bone ; human femur ; a, Haversian canal in cross-section ; a>, Haversian canal occupied by debris; a", anastomosing branch from a', m nearly longitudinal section ; b, lacuna belonging to the Haversian system, of which a occupies the centre : c, lacuna in excentric laminae of bone between the Haversian systems. The delicate lines connecting the lacunae are the canaliculi. (Dunham.)

structure of bone is well shown ; and likewise when the organic matter is burned away {calcinatioii) there is left an exact picture of bone structure.

There are two varieties of bone, the compact and the cancello'iu^ or spongv, the former being dense and hard, while the latter resembles the framework of a sponge. The periosteum, the enveloping membrane of bone, is composed of two layers, an outer dense fibrous, and an inner cellular or osteogenetic layer.

COMPACT BONE— BONE-MARROW.

Compact bone forms tlie shafts of the long bones and the outer part of the flat and irregular bones. It is composed of a system of tubes, called the Haversian canals, surrounded by a series of concentric lameUcc or bone-plates. These canals, which connect with the central marrow-cavity, supply nutrition to the bone and contain blood, lymph, and marrow.

Between the various lamellje are small spaces called lacunce, or little lakes, and connected with these are small canals, the canal iculi.

The lacunae contain the hone-cells or corpuscles, and their branches extend into the canaliculi, thus receiving their nutrition. The laciime are arranged in rows more or less parallel with the Haversian canals.

The lamellae are arranged, in the shaft of long bones, into three sets : (1) The general ov fundamental, those beneath the periosteum and surrounding the medullary canal. (2) The Haversian, which are arranged concentrically around the Haversian canals. (3) The interstitial, which are between the Haversian systems, filling the spaces between adjacent Haversian systems.

Certain fibres ])ierce the lamellae vertically to the surface of the bone and hold the plates together. These are called the perforating fibres of Sharpeg.

Cancellous or spongy bone occurs in the ends of the long bones and the centres of the flat or irregular bones. It is of a less dense structure, and the large cavities are filled with marrow from which it derives its nourishment, not having such a com])lete system of vessels as in the compact variety.

Bone-marrow is a soft vascular tissue found in the medullary canal, the cancdlous ends of bones, and the Haversian canals. It is divided into the red and the yellow marroiv.

Bed marrow occurs in the ends of long bones, in the bodies of the vertebra), and in the cavities of the flat bones in adults and throughout the bones in the young.

The red jnarrow is a lym])hoid organ, and is probably the main source of the formation of the red blood-cells.

It is composed of a delicate connective- tissue reticulum with a capillary network, in the meshes of which are the

BONE.

maiTow-cells, resembling leucocytes, and divided into eosinopliiles, myelocytes, erythroblasts, and basopliiles. Many of these maiTow-cells contain pigment-granules, which are tlie remains of disintegrated red blood-cells. The red marow contains few fat-cells, and bloodvessels and nerves are found only in small numbers.

Section of red marrow ; human : a. a, erythroblasts ; b, b, myelocytes ; b', myelocyte undergoing division; c, giant cell with a single nucleus: c', giant cell with dividing nucleus: d, reticulum: c, space occupied by a fat-cell (not represented); /, granules in a portion of an acidophilic cell. (Bohm and Davidofh)

Yellow metrrow differs from the red only in that it contains large quantities of fat-cells, to which it owes its color. It arises from the red marrow by a diminution of the marrowelements and l)y an increase in fit.

Dentine resembles bone except that it is devoid of Haversian canals and lacume, and has long, parallel tubules in place of canaliculi.

BONE DEVELOPMENT.

Bone Development. — This occurs by two methods, tlie cartilaginous and the mcmhi'anous.

Cartilaginous Development of Bone. — Most of the bones of the body, except those of the head, are first modelled in hyaline cartilage and covered with the perichondrinm or early

Fig. 2G.

Development of bone, cartilaginous method. (Klein.)

periosteum. The process is best divided into the following stages :

Proliferation and Cahifimtion. — The cartilage-cells at certain ]daces in the bones begin to arrange themselves in rows, enlarge, and a deposition of lime salts oceurs known as centres of ossification. The hyaline matrix is transformed into a number of ealeified trabeeulte inelosing spaces

BONE.

called the primary areolce., in which are the cartilage-cells. These soon gradually disintegrate and disappear.

Vascularization of Cartilage. — The cellular layer of the periosteum, containing the osteoblasts, now sends processes into the substance of the cartilage, and bloodvessels are formed wdiich penetrate the calcified trabeculae and enlarge the areolae.

Cartilage changed to Embryonic Bone. — The osteoblasts now surround the trabeculae and deposit several layers of bone in concentric lamellae as in the Haversian system, and the calcified cartilage is now changed to spongy bone.

Spongy Bone changed to Periosteal Bone. — Larger bone-forming cells now appear, called the osteoclasts, and these destroy some of the spongy bone and construct the central or medullary canal. The periosteum also deposits layers of bone on the circumference of the shaft and the spongy bone is changed to periosteal bone.

Formation of Compact Bone. — This is effected by the osteoblasts developing layers around the spongy bone, and dense bone gradually replaces the early embryonic bone. The long bones increase in length by the growth at the ends of the shaft, which is an advance of the process of ossification of the cartilage between the diaphysis and epiphysis.

Membranous Development of Bone. — Most of the bones of the skull are developed in connective tissue by a deposition of lime salts in the bundles of connective tissue along the surface. In these bundles the cells have arranged themselves in a layer, and becoming rich in protoplasm are converted into osteoblasts. The cellular layer of the periosteum sends out processes, called osteogenetic spiculae, of a bony nature and surrounded with bone-forming cells, which secrete layers of bone as in the formation of the lamellae of the Haversian svstern. The tissue becomes more vascular and the osteoclasts absorb the spongy bone to make marrow-cavities, while the dense bone is deposited from the periosteum.

QUESTIONS.

What is cartilage ? Name the three varieties.

Describe hyaline cartilage.

What is fibrocarttlage ?

THE MUSCULAR TISSUES.

What is elastic cartilage?

What is bone?

Describe the periosteum.

Name the two varieties of bone.

Where is compact bone found?

Name the parts of an Haversian system.

What are the lamella}? The lacuna}? The caualiculi?

Where do you tind spongy bone?

Name the kinds of bone-marrow.

Describe red marrow.

Describe yellow marrow.

Name the two methods of bone development.

Name the stages of the cartilaginous method. Describe each stage. Describe the membranous method.