Part 92

The =apex= occupies the central angle of the concave border of the sole, and forms a blunt, round prominence a little in front of the middle of the ground surface of the hoof.

=Structure of the Hoof.=—The hoof is composed of epithelial cells which are more or less completely keratinized except in its deepest part, the =stratum germinativum=; here the cells have not undergone cornification, and by their proliferation maintain the growth of the hoof. The cells are in part arranged to form tubes which are united by intertubular epithelium, and inclose medullary cells and air-spaces.

The =wall= may be regarded as consisting of three layers. The external layer consists of the periople and the stratum vitreum. The =periople= is composed of soft, non-pigmented tubular horn. It is continuous with the epidermis above, and extends downward a variable distance. Usually it forms a distinct band somewhat less than an inch wide, except at the heels, where it is much wider, and caps the angle of inflection of the wall proper. The =stratum vitreum= is a thin layer of horny scales which gives the wall below the periople its smooth, glossy appearance. The =middle= or =tubular layer= forms the bulk of the wall, and is the densest part of the hoof. Its horn tubes run in a straight direction from the coronary to the ground border. In dark hoofs it is pigmented except in its deep part. The internal or laminar layer consists of the =primary= and =secondary laminæ= and is non-pigmented. The laminæ are narrow and thin at their origin at the lower margin of the coronary groove, but become wider and thicker below. At the junction of the wall and sole they are united by interlaminar horn to form the white line. Only the central part of the laminæ becomes fully keratinized. They are composed of non-tubular horn in the normal state.

The =sole= consists of tubular and intertubular horn. The tubes run parallel with those of the wall and vary much in size.

The =frog= is composed of relatively soft horn, which is much more elastic than that of the wall or sole, and is not fully keratinized. The horn tubes in it are slightly flexuous.

The hoof is non-vascular and receives its nutrition from the matrix. It is also destitute of nerves.

THE MATRIX OF THE HOOF

The =matrix= of the hoof (Matrix ungulæ) is the specially modified and highly vascular part of the corium of the common integument which furnishes nutrition to the hoof. It is convenient to divide it into five parts which nourish corresponding parts of the hoof.

1. The =perioplic matrix= or =ring= (Margo matricis ungulæ) is a band 5 to 6 mm. in width which lies in a groove between the periople and the coronary border of the wall. It is continuous above with the corium of the skin, and is marked off by a groove from the coronary matrix. At the heels it widens and blends with the matrix of the frog. It bears very fine, short papillæ which curve downward and are received in depressions of the periople, to which it supplies nutrition.

2. The =coronary matrix= or =cushion= (Corona matricis ungulæ) is the thick part of the corium which occupies the coronary groove, and furnishes nutrition to the bulk of the wall. It diminishes in width and thickness posteriorly, and along the upper border of the bar it is not very clearly defined from the matrix of the frog. The convex superficial surface is thickly covered with papillæ 4 to 6 mm. in length, which are received into the funnel-like openings of the coronary groove. At the heels and along the bars the papillæ are arranged in rows, separated by fine furrows. The deep surface is attached to the extensor tendon and the lateral cartilages by an abundant subcutis which contains many elastic fibers and a rich venous plexus.

3. The =laminar matrix= (Latus matricis ungulæ)—also termed the sensitive laminæ—bears primary and secondary laminæ which are interleaved with the horny laminæ of the wall and bars in the natural state. It is attached to the wall surface of the third phalanx by a modified periosteum (Stratum periosteale) which contains a close-meshed network of vessels, and to the lower part of the lateral cartilages by a subcutis which contains a rich venous plexus. The laminæ are small at their origin above, become wider below, and end in several papillæ 4 to 5 mm. in length. The sensitive laminæ supply nutrition to the horny laminæ and to the interlaminar horn of the white line.

4. The =sole matrix= (Latus volare matricis ungulæ)—also termed the sensitive sole—corresponds to the horny sole, to which it supplies nutrition. It is often more or less pigmented and bears long papillæ, which are specially large along the convex border and at the angles. Centrally it is continuous with the matrix of the frog and bars. The deep surface is attached to the sole surface of the third phalanx by a modified and highly vascular periosteum.

5. The =frog matrix= (Furca matricis ungulæ)—also called the sensitive frog—is moulded on the deep surface of the frog and bears small papillæ. Its deep face is blended with the plantar cushion. The germinal cells of the frog derive their nutrition from this part of the matrix.

The =digital= or =plantar cushion= (Torus digitalis) is an important part of the elastic apparatus of the foot. It is a wedge-shaped mass which overlies the frog. It presents for description four surfaces, a base, and an apex. The =superior surface= faces upward and forward and is connected with the distal fibrous sheath of the deep flexor tendon. The =inferior surface=, covered by the matrix of the frog, is moulded on the upper face of the frog. The =lateral surfaces= are related chiefly to the lateral cartilages; inferiorly the cushion is closely attached to the cartilages, but higher up a rich venous plexus intervenes. The =base=, situated posteriorly, is partly subcutaneous, and is divided by a central depression into two rounded prominences termed the bulbs of the plantar cushion. The =apex= lies under the terminal part of the deep flexor tendon. The cushion is poorly supplied with vessels. It consists of a feltwork of fibrous trabeculæ and elastic fibers, in the meshes of which are masses of fat. The bulbs are soft and loose in texture and contain a relatively large amount of fat, but toward the apex the cushion becomes denser and more purely white fibrous in structure. Branched =coil glands= occur chiefly in the part of the cushion which overlies the central ridge of the frog. Their ducts pursue a slightly flexuous course through the matrix and pass in a spiral manner through the frog. Their secretion contains fat.

=Vessels and Nerves.=—The matrix is richly supplied with blood by the =digital arteries=. The =veins= are valveless, and form remarkable plexuses which communicate freely with each other and are drained by the digital veins. The =lymph vessels= form subpapillary plexuses in the matrix of the sole and frog, and a wider-meshed plexus at the base of the plantar cushion. A considerable lymph vessel lies in the attached edge of each of the laminæ. The =nerves= are branches of the digital nerves; some fibers end in lamellar corpuscles and end-bulbs.

The =ergot= is a small mass of horn which is situated in the tuft of hair at the flexion surface of the fetlock. It is the vestige of the second and fourth digits of extinct equidæ and hence is absent in cases in which these digits are developed. A small tendinous band, 3 to 5 mm. in width, extends downward and slightly forward from the fibrous basis of the ergot on each side, crosses over the digital vessels and nerves very obliquely, and blends below with the digital fascia and the plantar cushion. It is known as the ligament or tendon of the ergot.

The term =chestnut= is applied to the masses of horn which occur on the inner surface of the forearm about a handbreadth above the carpus, and on the lower part of the inner face of the tarsus. They have an elongated oval form and are flattened. They are regarded usually as vestiges of the first digit. That of the hind limb is absent in the donkey and very small in the mule.

These horny vestiges are quite variable in form and size and are correlated with the fineness or coarseness of the integument in general. The supracarpal chestnut is about 1½ to 2½ inches long, oval in outline, the proximal end being pointed; it overlies the flexor carpi internus at a quite variable distance above the carpus, and hence should not be used as a surgical landmark. The tarsal chestnut lies at a point behind the lower part of the internal lateral ligament of the hock. When well developed it is about 2 to 2½ inches long, broad below and produced above to form a long pointed end, with a short blunt anterior process. They are composed of horn somewhat like that of the frog.

ORGAN OF SMELL

The peripheral part of the olfactory apparatus or organ of smell (Organon olfactus) is that part of the nasal mucous membrane which was referred to in the description of the nasal cavity as the olfactory region; this (Regio olfactoria) is limited to the ethmoturbinals and the adjacent part of the superior turbinal and the septum nasi, in which the fibers of the olfactory nerve ramify. It is distinguished by its yellow-brown color, thickness, and softness. It contains characteristic tubular =olfactory glands= (of Bowman), which are lined by a single layer of pigmented cells, and a neuro-epithelium, the =olfactory cells=, the central processes of which extend as non-medullated fibers to the olfactory bulb.

The epithelium is non-ciliated and is covered by a structureless limiting layer. It consists essentially of three kinds of cells, supporting, basal, and olfactory. The supporting cells are of long columnar form above and contain pigment granules; below they taper and often branch, and their central processes unite with those of adjacent cells to form a protoplasmic network. The basal cells are branched and lie on a basement membrane. The olfactory cells are situated between the supporting cells; they have the form of long narrow rods, with an enlarged lower part which is occupied by the nucleus. The peripheral end pierces the limiting membrane and bears a tuft of fine hair-like cilia (olfactory hairs). A central process extends from the nucleated pole of the cell to the olfactory bulb as a non-medullated olfactory nerve-fiber.

The =vomero-nasal organ= (of Jacobson) lies along each side of the anterior part of the lower border of the septum nasi. It communicates with the nasal cavity through the naso-palatine canal. It consists of a tube of hyaline cartilage lined with mucous membrane; a small part of the latter along the inner side is olfactory in character.

THE ORGAN OF TASTE

The peripheral part of the gustatory apparatus (Organon gustus) is formed by the microscopic =taste buds= (Calyculi gustatorii), which occur especially in the foliate, fungiform, and vallate papillæ, in the free edge and anterior pillars of the soft palate, and the oral surface of the epiglottis. The taste buds are ovoid masses, which occupy corresponding recesses in the ordinary epithelium; each presents a minute opening, the gustatory pore. The buds consist of fusiform supporting cells grouped around central =gustatory cells=. The latter are long and narrow; the peripheral end of each bears a small filament, the gustatory hair, which projects at the gustatory pore; the central end is produced to form a fine process which is often branched. The taste buds are innervated by fibers of the glosso-pharyngeal nerve and the lingual branch of the trigeminus.

SENSE ORGANS AND SKIN OF THE OX

THE EYE

The =eyelids= are thick, prominent, and less pliable than those of the horse. The lower lid bears a considerable number of cilia, which are, however, finer than those of the upper lid. The tarsal glands are more deeply embedded and therefore not so evident. The =conjunctiva= of the lower lid presents folds or ridges, and one or two prominences which contain numerous leukocytes; the conjunctival epithelium is transitional in type. The superficial part of the cartilage of the =third eyelid= is leaf or shovel-shaped and thicker than in the horse; the edge bears a narrower process, on which there is a transverse bar, giving the arrangement some resemblance to an anchor. The =gland= of the third eyelid is very large—an inch or more in length—and may be divided into two parts. The deep part is pink and consists of loose lobules, but the much larger superficial part is more compact. There are two large and several smaller excretory ducts. The subconjunctival tissue of the third eyelid contains lymph nodules, which are specially numerous on the bulbar side.

The =lacrimal gland= is thick and distinctly lobulated. It is more or less clearly divided into a thick upper and a thinner lower part (Glandula lacrimalis superior, inferior). There are six to eight larger excretory ducts and several smaller ones. The =naso-lacrimal duct= is shorter than in the horse, and is almost straight. Its terminal part is inclosed between two plates of cartilage, and it opens near the nostril on the outer wall; the orifice is placed on the inner side of the alar fold of the inferior turbinal, and is therefore not easily found.

The =eyeball= resembles that of the horse in shape, but is considerably smaller.

The average transverse diameter is about 42 mm., the vertical diameter 41 mm., and the axis 36 mm. The angle between the axes is about 119°.

The =sclera= is often more or less pigmented; where non-pigmented it may have a bluish tinge. The point of entrance of the optic nerve is about 2 mm. external to the vertical meridian, and about 7 mm. below the horizontal meridian.

The thickness of the sclera is about 2 mm. at the posterior pole, 1 mm. at the equator, and 1.2 to 1.5 mm. near the cornea.

The =cornea= is thicker than that of the horse.

The =tapetum= of the chorioidea is extensive at the outer side, but is a narrow strip internally. It has a metallic luster, shading from a brilliant green to a deep blue; centrally it has a reddish sheen.

The =iris= is usually very dark colored. The granula form a continuous series of small nodules along the upper margin of the pupil and are most prominent centrally; they are very small on the lower margin.

The =optic papilla= is much smaller and is not so sharply defined on ophthalmoscopic examination as that of the horse. Several relatively large retinal arteries radiate from the center of the papilla to the periphery of the retina. They may be seen to wind spirally around the veins, which are very large.

The arteria centralis retinæ arises from a posterior ciliary artery and divides close to the optic papilla into three branches usually; of these the upper is larger than the two lateral branches. The retina is more vascular than that of the horse; it has a round area centralis at the inner side, which is continued outward by a narrow strip of a similar histological structure.

The =vitreous body= is less fluid than that of the horse.

THE EAR

The =external ear= is inclined outward. The middle part is much wider and less curved than in the horse. The apex is also wide and does not curve forward. The lower part of the anterior border is bent backward and bears long hairs. The posterior border is thin and is regularly convex, except below, where it is indented. The opening is wide and the concave surface presents four ridges; the convex surface presents corresponding depressions. The styloid process of the conchal cartilage is short and blunt. The edges of the annular cartilage are in contact at the inner side and the upper border is notched externally. The scutiform cartilage is a very irregular quadrilateral plate; it is situated on the lateral aspect of the cranium with its concave surface in contact with the fat and temporalis muscle. The osseous external auditory meatus is directed practically straight inward; it is about twice as long as that of the horse, and tapers very gradually from without inward. The chief special characters of the =auricular muscles= are as follows: (1) The scutularis blends with the frontalis muscle. The interscutularis arises from the base of the processus cornu (or the corresponding area in polled cattle) and from the frontal crest. (2) The cervico-scutularis arises from the posterior surface of the cranium below the frontal eminence, and receives slips from the parieto-auricularis and cervico-auricularis superficialis. (3) The zygomatico-auricularis and scutulo-auricularis superficialis inferior are fused. (4) The scutulo-auricularis superficialis superior is distinct from the interscutularis; it arises from the superficial face of the scutiform cartilage. (5) The cervico-auricularis superficialis arises from the ligamentum nuchæ and ends on the convex surface of the conchal cartilage. (6) The parieto-auricularis arises from the nuchal surface of the frontal bone, the adjacent part of the parietal bone, and the ligamentum nuchæ; it is inserted below the preceding muscle. (7) The scutulo-auricularis superficialis accessorius arises from the superficial face of the scutiform cartilage and is inserted by a round tendon into the anterior part of the convex surface of the conchal cartilage. (8) The cervico-auricularis profundus minor consists of two fasciculi; the inner, narrow part is deep red in color, and arises from the fascia of the cervical muscles external to the occipital attachment of the ligamentum nuchæ; the outer, wider part is pale, and arises beneath the cervico-auricularis superficialis, indirectly from the scutiform cartilage. The two unite and are inserted into the lower aspect of the base of the conchal cartilage. (9) The scutulo-auricularis profundus minor arises from the temporal crest above the external auditory meatus and is inserted into the anterior part of the deep face of the scutiform cartilage.

The =cavum tympani= is small; it communicates ventrally with the air-cells of the bulla ossea. The tympanic membrane is nearly circular and is not so oblique as in the horse. The auditory ossicles are smaller than those of the horse; the malleus is more curved, the body of the incus is longer, and there is a small prominence on the front of the head of the stapes for the attachment of the stapedius muscle.

The =Eustachian tube= is small and is only about two inches long. The pharyngeal opening is small and is situated on the side of the fornix of the pharynx close to the base of the cranium. There is no flap-like expansion of the cartilage, but the inner border of the orifice is formed by a fold of mucous membrane.

The =internal ear= has essentially the same arrangement as in the horse.

COMMON INTEGUMENT

The thickness of the =skin= of the ox is greater than that of any of the other domesticated animals; in general it is about 3 to 4 mm., but at the root of the tail and the point of the hock it is about 5 mm. and on the brisket 6 to 7 mm. The variably developed prominence at the anterior part of the pectoral region known as the brisket consists of a fold of skin (Plica colli ventralis longitudinalis), which contains posteriorly a mass composed of coarse fibrous trabeculæ and fat.

The =cutaneous glands= are fewer and less developed than in the horse. Except about the natural openings, at the point of the hock, and the flexion surface of the fetlock, the =sweat glands= do not form a coil, but are enlarged at the deep end and are variably flexuous. The =sebaceous glands= are best developed about the natural openings and on the udder, but there are none on the teats. The =naso-labial glands= form a thick layer under the bare skin of the muzzle. They are compound tubular glands and are lined with cubical epithelium. The openings of their excretory ducts are easily seen.

The =hairs= are extremely variable in color and size in the different breeds and in different individuals. The hair of the frontal region is often curly, especially in the bull. There is no mane, and the long hairs of the tail occur only at the end, where they form the “brush” (Cirrus caudæ).

The =claws=, four in number on each limb, cover the ends of the digits. Those of the chief digits conform in a general way to the shape of the third phalanges, and each may be regarded as having three surfaces. The abaxial or outer surface is convex from side to side, and is marked by ridges parallel with the coronary border. Its anterior part is concave from edge to edge, and the angle which it forms with the ground is about 30°. The interdigital or inner surface is concave and grooved; it touches the opposite claw only at its ends. The inferior or ground surface consists of two parts, viz., a slightly concave sole, which is pointed in front and widens behind, and a prominent bulb of soft thin horn, which is continuous above with the skin. The claw may be regarded as consisting of three parts—periople, wall, and sole. The periople surrounds the coronary border in the form of a flat band, which is about half an inch wide, except at the heels, where it widens to cover the entire surface. The wall forms most of the abaxial or outer part of the claw and is reflected in front upon the interdigital surface. It thins out toward the bulb or heel, which appears, as stated above, to consist of the thin expansion of the periople. The sole occupies the angle of inflection of the wall; it is continuous without demarcation with the periople of the bulb. The perioplic matrix bears relatively long papillæ. The coronary matrix is much less developed than in the horse and its papillæ are short. The sensitive laminæ are much narrower and are more numerous than in the horse; secondary laminæ are not present. The matrix of the sole is not marked off behind from that of the periople; its papillæ are very small and close together. The matrix of the bulbs is separated from the flexor tendon by a mass of elastic, fatty tissue, which is analogous with the plantar cushion of the horse. The papillæ here are long and often compound.