Part 42

=Structure.=—The spleen has an almost complete =serous coat=. Subjacent to this and intimately united with it is a =capsule= of fibrous tissue (Tunica albuginea), which contains many elastic fibers and some unstriped muscular tissue. Numerous =trabeculæ= (Trabeculæ lienis) are given off from the deep face of the capsule and ramify in the substance of the organ to form a supporting network. In the interstices of this framework is the =spleen pulp= (Pulpa lienis), a dark red, soft, grumous material. This is supported by a delicate adenoid =reticulum=, and contains numerous leukocytes, the large splenic cells, red blood-corpuscles, and pigment. The pulp is richly supplied with blood. The branches of the splenic artery enter at the hilus and pass along the trabeculæ. The arteries which enter the pulp have a sheath of lymphoid tissue, which collects on the vessel wall at certain points, forming small =lymph nodules=, the so-called Malpighian corpuscles (Noduli lymphatici lienales). These are visible to the naked eye as white spots, about as large as the head of a pin. The blood passes into cavernous spaces lined by endothelium which is continuous with the cells of the reticulum of the pulp. From these the veins arise. The splenic vein runs in the hilus in company with the artery and nerves, and joins the posterior gastric vein to form a large radicle of the portal vein.

=Blood-supply.=—Splenic artery.

=Nerve-supply.=—Splenic plexus.

THE PERITONEUM

The general disposition of the peritoneum has been described, and other facts in regard to it were mentioned in the description of the viscera. It is now desirable to study it as a continuous whole.[103] (Figs. 256, 257, 278, 279.)

We may consider the peritoneum as consisting of two sacs—a greater and a lesser. The =greater sac= lines the greater part of the abdominal cavity, and covers most of the viscera which have a peritoneal investment. The =lesser sac= is an introversion or recess of the greater sac, formed during the development of the viscera. The two sacs communicate by a relatively narrow passage, termed the =epiploic foramen= of Winslow (Foramen epiploicum). This opening is situated on the visceral surface of the liver above the portal fissure. It can be entered by passing the finger along the caudate lobe of the liver toward its root. Its dorsal (or anterior) wall is formed by the caudate lobe and the posterior vena cava. Its ventral (or posterior) wall consists of the pancreas, the gastro-pancreatic fold, and the portal vein. The walls are normally in contact, and the passage merely a potential one. It is usually about four inches (ca. 10 cm.) in length. It is narrowest at the right extremity, where it is about an inch (ca. 2.5 to 3 cm.) wide.[104] If the finger is passed into the foramen from right to left, it enters the cavity of the lesser sac. If now an opening is made in the great omentum and the other hand introduced through it, the fingers of the two hands touch each other over the lesser curvature of the stomach. The formation and boundaries of the lesser sac should now be examined by spreading out the great omentum. It will be found that the latter now incloses a considerable cavity behind the stomach; this is termed the =omental cavity= (Bursa omentalis). Passing forward over the lesser curvature of the stomach, we enter another space, the =vestibule= of the omental cavity (Vestibulum bursæ omentalis). This space is closed on the left by the gastro-phrenic ligament, below and on the right by the lesser omentum, and dorsally by the gastro-pancreatic fold, which is attached to the dorsal border of the liver and to the posterior vena cava. Above the œsophageal notch the fingers can be passed around the border of the liver and the vena cava till the coronary ligament is encountered. Thus the vestibule is closed except (1) on the right, where it communicates with the cavity of the greater sac by the epiploic foramen; and (2) behind, where it communicates with the cavity of the omentum.

[Illustration:

FIG. 278.—DIAGRAM OF GENERAL ARRANGEMENT OF PERITONEUM (OF MARE) IN SAGITTAL TRACING.

_a_, Pouch between rectum and roof of pelvis, continuous with _b_, recto-genital pouch; _c_, vesico-genital pouch; _d_, pouch below bladder and its lateral ligaments; _f_, lesser omentum; _Int._, small intestine. The arrow points to the epiploic foramen (of Winslow). ]

The general arrangement of the great omentum has already been indicated. We may now trace its line of attachment, which would correspond to the mouth of the sac. Beginning at the ventral part of the great curvature of the stomach, the line passes to the ventral face of the pylorus, then crosses obliquely the first part of the duodenum to the point where the pancreas is adherent to it. Here it passes to the anterior face of the terminal transverse part of the great colon, runs along this transversely (from right to left), and continues for some ten or twelve inches (ca. 25 to 30 cm.) on the small colon. It then forms an acute angle, passes inward and forward along the small colon to the dorsal part of the hilus of the spleen, where it blends with the suspensory ligament of the latter, and forms a recess (Recessus lienalis) behind the saccus cæcus of the stomach. It now passes along the hilus of the spleen, and is continued to the great curvature of the stomach by the gastro-splenic omentum. It is convenient to regard the spleen as being intercalated in the left part of the great omentum; on this basis the gastro-splenic omentum would be that part of the great omentum which connects the hilus of the spleen with the great curvature of the stomach. The great omentum is relatively small in the horse, and is usually not visible when the abdomen is opened. It is generally folded up in the space between the visceral surface of the stomach and the intestine.[105]

The lesser sac furnishes the peritoneal covering for: (1) the visceral surface of the stomach and a small area of the first curve of the duodenum; (2) a large part of the dorsal surface of the pancreas and portal vein; (3) a small part of the visceral surface of the liver above the attachment of the lesser omentum and the portal fossa; (4) the posterior vena cava, from the level of the epiploic foramen [of Winslow] to its passage through the diaphragm (in so far as it is not embedded); (5) the part of the parietal surface of the liver between the right and middle divisions of the coronary ligament; (6) the corresponding part of the diaphragm, and the right part of the right crus of the same; (7) part of the anterior surface of the terminal part of the great colon, and the origin of the small colon; (8) the left extremity of the pancreas (inconstant); (9) the spleen.

We may now trace the peritoneum in a longitudinal direction, beginning in front. It is reflected from the ventral abdominal wall and the diaphragm upon the liver, forming the ligaments and serous coat of the gland. It leaves the visceral surface of the liver as lesser omentum, and the crura of the diaphragm as the gastro-phrenic ligament, reaches the saccus cæcus and lesser curvature of the stomach and the first curve of the duodenum, covers these organs, and is continued by the great omentum.

[Illustration:

FIG. 279.—DIAGRAM OF ABDOMINAL PERITONEUM IN FRONTAL (HORIZONTAL) TRACING.

_D_, Duodenum. The arrow indicates the epiploic foramen (of Winslow). By an oversight the leader line to the great omentum is omitted, and the coronary ligament of the liver is erroneously marked lesser omentum; the latter extends from liver to stomach, but is not marked. ]

On the left it passes from the left crus of the diaphragm and the left kidney to form the suspensory ligament of the spleen, clothes that organ, and leaves it to be continued by the great omentum.

On the right it passes from the right crus of the diaphragm and the dorsal border of the liver to the concave border of the duodenum, forming the gastro-pancreatic fold (second part of the mesoduodenum), and covering part of the dorsal surface of the pancreas. From the margin of the pancreas, the right kidney, and a small area of the sublumbar region behind the latter, it passes on to the base of the cæcum and the terminal part of the great colon. From these it passes on the right to the duodenum, forming the third part of the mesoduodenum. On the left it clothes part of the ventral surface and the outer border of the left kidney, from which it passes to the base of the spleen, forming the ventral layer of the suspensory ligament of the latter. Behind the terminal part of the great colon it is reflected around the great mesenteric artery to form the great mesentery. Behind this it is reflected almost transversely from the roof of the cavity and from the origin of the small colon on to the duodenum, forming the terminal part of the mesoduodenum. The line of origin of the colic mesentery begins on the inner part of the ventral surface of the left kidney, and extends to the sacral promontory, where the mesorectum begins. At the termination of the latter the peritoneum is reflected from the rectum on the dorsal and lateral walls of the pelvic cavity. Below the rectum it forms the urogenital fold, and passes on to the dorsal surface of the bladder, covers its anterior part, and is reflected on to the body-wall laterally and ventrally, forming the lateral and middle ligaments of the bladder. In the female the broad ligaments of the uterus replace the urogenital fold, with which they are homologous.

In the new-born foal certain folds are specially large. The falciform ligament of the liver extends to the umbilical opening, and contains in its free edge the large umbilical vein. The bladder—at this time an abdominal organ—has a ventral median fold, which connects it and the urachus with the abdominal floor. This is flanked on either side by a fold which also extends to the umbilicus, and contains the large umbilical artery.

DIGESTIVE SYSTEM OF THE OX

THE MOUTH

The cavity of the mouth is shorter and wider than that of the horse, and the vestibule is more capacious.

[Illustration:

FIG. 280.—ANTERIOR PART OF LOWER JAW OF OX.

_60_, Tip of tongue. (After Ellenberger-Baum, Anat. für Künstler.) ]

The =lips= are thick, wide, and comparatively immobile. The middle part of the upper lip and the surface between the nostrils is bare, and is termed the muzzle (Planum nasolabiale). It is smooth, and (in health) is kept cool and moist by a clear fluid secreted by a layer of subcutaneous glands (Glandulæ nasolabiales) about half an inch (ca. 1.5 cm.) thick. It shows irregular lines, mapping out small polygonal areas on which the orifices of the gland-ducts are visible. A narrow bare strip also exists along the edge of the lower lip. The remainder of the integument is provided with ordinary and tactile hairs. The free edge and the lining membrane present verrucose, horny papillæ. The labial glands form compact masses near the angles of the mouth.

The =cheeks= are more capacious than in the horse. The mucous membrane presents large conical pointed =papillæ=, which are directed toward the fauces and are covered with a horny epithelium. The largest of these have a length of about half an inch (ca. 1 to 1.5 cm.) and are situated around the angle of the mouth and parallel with the cheek teeth. The orifice of the parotid duct is opposite the fifth upper cheek tooth. (In the sheep and goat it is opposite the fourth tooth.) The =buccal= or =molar glands= are very well developed, and are arranged in three parts. The dorsal row extends from the maxillary tuberosity to the angle of the mouth. Its lobules are of a light yellow color. The ventral part consists of a compact brownish mass which reaches from the angle of the mouth a short distance under the masseter muscle. The middle part consists of loosely arranged yellow lobules.

[Illustration:

FIG. 281.—SAGITTAL SECTION OF HEAD OF COW, CUT A LITTLE TO THE RIGHT OF THE MEDIAN PLANE.

_1_, Cerebral hemisphere; _2_, corpus striatum; _3_, hippocampus; _4_, olfactory bulb; _5_, corpora quadrigemina; _6_, optic nerve; _7_, pons; _8_, medulla oblongata; _9_, spinal cord; _10_, pituitary body; _11_, sphenoid sinus; _12_, lateral mass of ethmoid; _13_, ventral straight muscles; _14_, pharyngeal (retropharyngeal) lymph gland; _15_, longus colli; _16_, soft palate; _17_, vallate papillæ; _18_, tonsillar sinus; _19_, conical papillæ of cheek; _20_, hyo-epiglotticus muscle; _21_, epiglottis; _22_, hyo-glossus muscle; _C1_, _C2_, atlas, axis. Subject was hardened with mouth open. ]

A linear series of large papillæ exists on the floor of the mouth on each side of the frenum linguæ. Near these are found the openings of the small ducts of the sublingual gland. The papilla on which the submaxillary duct opens is wide, hard, and has a serrated edge.

The =hard palate= is wide, and is usually more or less pigmented. The body of the premaxilla is covered with a thick layer of dense connective tissue, which has a thick, horny epithelial covering—forming the so-called dental plate or pad. The palatine ridges extend from this backward about two-thirds of the length of the hard palate. They are nearly straight, and, for the most part, are serrated on the free edge. A median furrow extends between the ridges. The posterior third of the palate is smooth. Between the dental plate and the first ridge is the triangular papilla incisiva; on either side of this is a deep furrow, in which is the oral opening of the =naso-palatine canal=. This canal is two inches or more (ca. 5 to 6 cm.) in length and opens on the floor of the nasal cavity; it also communicates by a slit-like opening with the organ of Jacobson.

[Illustration:

FIG. 282.—CROSS-SECTION OF HEAD OF OX.

The section passes through the internal canthi. _L.a._, Lingual arteries. The arrow indicates the communication between the maxillary and palatine sinuses. ]

The =soft palate= is somewhat shorter than that of the horse, but is long enough to close the isthmus of the fauces. The posterior pillars do not extend to the entrance of the œsophagus. The azygos muscle is much better developed than in the horse. The fibrous aponeurosis is for the most part replaced by muscular tissue.

The =isthmus faucium= is wide and dilatable. On either side, behind the anterior pillar of the soft palate, is a deep depression, the =sinus tonsillaris=; external to this is the compact bean-shaped tonsil, which is about one to one and a half inches (ca. 3 to 4 cm.) in length. The tonsil does not project into the fauces, but outward instead: hence it does not occupy the tonsillar sinus, and is not visible internally, as is the case in most animals.

[Illustration:

FIG. 283.—TONGUE OF OX, DORSAL ASPECT.

Pharynx, soft palate, and origin of œsophagus are cut dorsally and reflected. ]

THE TONGUE

The tongue of the ox is often variably pigmented. The root and body are wider than that of the horse, but the free part is more pointed. The posterior part of the dorsum forms a remarkable elliptical prominence, which is sharply defined in front. The filiform papillæ in front of this prominence are large and horny, with sharp points directed backward. They impart to the tongue its rasp-like roughness. The papillæ on the prominence are large, broad and horny; some have a blunt conical form, others are rounded or flattened. Behind the prominence, the papillæ are long and soft, _i. e._, not horny. The fungiform papillæ are numerous and distinct; they are scattered more generally over the dorsum and edges of the free part. The vallate papillæ are about twenty or thirty in number; they are smaller than those of the horse, and are irregularly distributed on either side of the posterior part of the prominence of the dorsum. The foliate papillæ and the lingual fibrous cord are absent. The muscles are well developed; the hyo-glossus arises by additional portions from the great and middle cornua of the hyoid bone. The tongue is highly protractile and is the chief organ of prehension.

THE TEETH

The dental formula of the ox is:

( 0 0 3 3 ) 2 ( I - C - P - M - ) = 32 ( 4 0 3 3 )

The =incisors= are absent from the upper jaw. There are eight incisors in the lower jaw, arranged in a somewhat fan-like manner. They are simple teeth, without infundibulum. The crown is white, short, and shovel-shaped. The root is rounded, and is embedded in the jaw in such a manner as to allow a considerable degree of movement. There is a distinct =neck=. In addition to the simple numerical designation, the following terms are commonly applied to the individual teeth: pinchers or central, first intermediate, second intermediate, and corner incisors. It is probable that the latter are much modified canines. The incisors of the ox do not advance out of the alveoli, as is the case in the horse; in old age, however, the gum retracts so that the roots are partly exposed and may come into wear.[106]

[Illustration:

FIG. 284.—INCISOR TEETH OF OX, LINGUAL ASPECT.

_C.s._, Caruncula sublingualis. ]

[Illustration:

FIG. 285.—INCISOR TOOTH OF OX.

_24′_, Lingual surface of crown; _24″_, masticatory surface. The crown is clearly marked off from the rounded root by a neck. (After Ellenberger-Baum, Anat. für Künstler.) ]

The =deciduous incisors= differ from the permanent set chiefly in being much smaller. The crowns are narrower and diverge more.

The =canines= are absent (unless the fourth incisors be considered to represent them).

[Illustration:

FIG. 286.—SKULL OF OX TWO YEARS OF AGE, SCULPTURED TO SHOW THE EMBEDDED PARTS OF THE TEETH.

_11–4_, Permanent incisor teeth, the third and fourth not erupted; _Di.3, 4_, third and fourth deciduous incisors; _P1–3_, upper permanent premolars, only first erupted; _Dp.2, 3_, deciduous premolars; _M1–3_, molars. ]

The =cheek teeth= (Fig. 286) resemble those of the horse in number and general arrangement. They are, however, smaller, and also differ in the fact that they progressively increase in size from before backward. This feature is so marked that the first tooth is quite small, and the space occupied by the first three (_i. e._, the premolars) is only about one-half of that required for the posterior three (_i. e._, the true molars). The enamel folds stand out even more prominently in relief on the masticatory surface than in the horse. The occurrence of wolf-teeth is rare.

The formula of the deciduous teeth is:

( 0 0 3 ) 2 ( Di — Dc — Dp — ) = 20 ( 4 0 3 )

TABLE OF AVERAGE PERIODS OF ERUPTION OF THE TEETH IN THE OX │ TEETH │ ERUPTION │ _A._ _Temporary:_ │ First incisor (Di 1) │Birth to 3 weeks. Second incisor (Di 2) │ „ Third incisor (Di 3) │ „ Fourth incisor (Di 4) │ „ ──────────────────────────────┼────────────────── First cheek tooth (Dp 1) │Birth to 3 weeks. ──────────────────────────────┼────────────────── Second cheek tooth (Dp 2)│Birth to few days. Third cheek tooth (Dp 3) │ „ ──────────────────────────────┼────────────────── │ _B._ _Permanent:_ │ First incisor (I1) │1½ to 2 years. Second incisor (I2) │2 to 2½ years. Third incisor (I3) │3 years. Fourth incisor (I4) │3½ to 4 years. First cheek tooth (P1) │2 to 2½ years. Second cheek tooth (P2) │1½ to 2½ years. Third cheek tooth (P3) │2½ to 3 years. Fourth cheek tooth (M1) │5 to 6 months. Fifth cheek tooth (M2) │1 to 1½ years. Sixth cheek tooth (M3). │2 to 2½ years.

The eruption of the permanent teeth is subject to great variation. The above figures are the average of observations of improved breeds under favorable conditions.

THE SALIVARY GLANDS

The =parotid gland= is smaller than that of the horse, and is light red-brown in color. It has somewhat the form of a very narrow long triangle, and lies chiefly on the posterior part of the masseter muscle. The thick wide upper end partly covers a large subparotid lymph gland. The small lower end is bent forward and fits into the angle of union of the jugular and external maxillary veins; it lies on the submaxillary gland. The parotid duct leaves the lower part of the deep face; in its course it resembles that of the horse, but it pierces the cheek opposite the fifth upper cheek tooth.

The =submaxillary gland= is very large, and is pale yellow in color. It is covered to a small extent by the parotid. Its general form resembles that of the horse, but its lower (or anterior) end is large and rounded, and is separated by a small interval only from the gland of the other side. This part can be distinctly felt in the living animal, and is related externally to a large submaxillary lymph gland. The duct leaves the middle of the superficial face of the gland, crosses the stylo-hyoideus and the intermediate tendon of the digastricus, and is then disposed as in the horse.

The =sublingual gland= consists of two parts. The dorsal part (Glandula sublingualis parvicanalaris) is long, thin, and pale yellow in color. It extends from the anterior pillar of the soft palate about to the symphysis of the jaw. It has numerous small tortuous ducts (Ductus sublinguales minores), which open between the papillæ under the side of the tongue. The ventral part is shorter and thicker, and is salmon pink in color. It has a single duct (Ductus sublingualis major), which either opens alongside of or joins the submaxillary duct.

THE PHARYNX

The pharynx is short and wide. The vault (Fornix pharyngis) is divided into two cul-de-sacs by a median fold of mucous membrane (Septum nasi membranaceum), which is a continuation of that of the septum nasi; on the outer wall of each is the relatively small opening of the Eustachian tube, which is covered by a simple fold of mucous membrane. The posterior nares are small. The entrance to the œsophagus is large.

[Illustration:

FIG. 287.—SALIVARY GLANDS OF OX.

_a_, Parotid gland; _b_, submaxillary gland; _c_, inferior, _d_, middle, and _e_, superior buccal glands; _f_, labial glands; _g_, buccinator nerve; _h_, buccinator vein; _1_, masseter (cut); _2_, ramus of mandible; _3_, zygomaticus muscle; _4_, conical papillæ of lip; _5_, buccinator muscle. (After Ellenberger, in Leisering’s Atlas.) ]

On the dorsal wall of the pharynx are two large pharyngeal lymph glands, which, when enlarged, cause difficulty in swallowing and breathing (Fig. 281).

THE ŒSOPHAGUS

This is much shorter, wider, and more dilatable than that of the horse. Its average diameter (when moderately inflated) is about two inches (ca. 5 cm.), and its length in a large animal is about three to three and a half feet (ca. 90 to 100 cm.). The wall is relatively thin, and the muscular tissue is striped throughout. The latter consists of two strata of spiral fibers, except near the stomach, where they are longitudinal and circular. Fibers are continued into the wall of the stomach for some distance. There are submucous glands in the first part of the tube. There is no terminal dilatation, and no part in the abdominal cavity.

A very large mediastinal lymph gland lies above the posterior part of the œsophagus and may, if enlarged, obstruct it (Fig. 289).

THE ABDOMINAL CAVITY