Part 45

The =spleen= (Fig. 301) is somewhat triangular, with the angles rounded off. It weighs about three or four ounces (ca. 100 grams). Its length is about five inches (ca. 12 to 13 cm.) and its greatest width about four inches (ca. 10 cm.). The parietal surface is convex and is related to the diaphragm, to which rather more than the anterior third is adherent. The visceral surface is concave and its anterior half is attached to the dorsal curvature of the rumen. The dorsal end or base is attached to the left crus of the diaphragm under the last two or three ribs. The hilus is at the posterior basal angle. The ventral end is narrower and thinner than the base; it is situated opposite the ninth and tenth ribs above their middles.

[Illustration:

FIG. 306.—LIVER OF SHEEP, PARIETAL SURFACE; HARDENED _in situ_. ]

DIGESTIVE SYSTEM OF THE PIG

THE MOUTH

The =rima oris= is extensive, the angles of the mouth being situated far back. The =upper lip= is thick and short, and is blended with the snout; the =lower lip= is small and pointed. The labial glands are few and small.

The mucous membrane of the =cheeks= is smooth. The =buccal glands= are compactly arranged in two rows opposite the cheek teeth. The =parotid duct= opens opposite the fourth or fifth cheek tooth.

The =hard palate= is long and narrow; it is marked by a median furrow, on each side of which are twenty or more ridges. On its anterior part there is a triangular incisive papilla, at which the naso-palatine ducts open.

The =soft palate= is very thick. Its direction almost continues that of the hard palate, _i. e._, it is nearly horizontal. It extends to the middle of the oral surface of the epiglottis.[110] It has a median prolongation termed the =uvula=. The oral surface presents a median furrow, on either side of which is an oval raised area, marked by numerous crypts; these elevations are the =tonsils=. Tonsillar tissue also occurs in the lateral walls of the fauces.

[Illustration:

FIG. 307.—TONGUE OF PIG.

_1_, Apex; _2_, dorsum; _3_, root; _a_, orifices of ducts of lingual glands; _b_, papillæ of root; _c_, vallate papilla (not really so distinct as in figure); _d_, foliate papilla; _e_, fungiform papillæ; _f_, epiglottis (pulled back); _g_, median glosso-epiglottic fold. (Ellenberger-Baum, Anat. _d_. Haustiere.) ]

The =tongue= is long and narrow and the apex is thin. Two or three vallate papillæ are present. The fungiform papillæ are small and are most numerous laterally. The filiform papillæ are soft and very small. On the root there are soft, long, pointed papillæ, directed backward. Foliate papillæ are also present.

There is a well-marked median glosso-epiglottic fold, on either side of which is a depression (Vallecula epiglottica). The frenum linguæ is double.

The =dental formula= of the pig is:

( 3 1 4 3 ) 2 ( I - C - P - M - ) = 44 ( 3 1 4 3 )

The formula for the temporary teeth is:

( 3 1 4 ) 2 ( Di - Dc - Dp - ) = 32 ( 3 1 4 )

The =upper incisors= are small; they are separated from each other by spaces, and from the canines by a larger interval. The first incisors are the largest, are convergent, and have no distinct neck. The second are narrower and somewhat smaller. The third (corner) incisors are much smaller, are flattened laterally, and have three small eminences on the crown.

The =lower incisors= are almost horizontal and are convergent and close together. The first and second are about equal in size, prismatic, and deeply implanted in the jaw. The labial surface is slightly convex, the lingual concave and marked near its extremity by a ridge. The third incisor is much smaller and has a short narrow crown and a distinct neck.

[Illustration:

FIG. 308.—SKULL OF PIG ABOUT A YEAR AND A HALF OLD, SCULPTURED TO SHOW THE EMBEDDED PARTS OF THE TEETH.

_I1–3_, Incisors; _C_, canines; _P1–4_, premolars; _M1–3_, molars. ]

The =canine teeth= or tusks of the male are greatly developed and project out of the mouth. The upper canine of the boar may be about three or four inches (ca. 8 to 10 cm.) long. The crown is conical and is curved somewhat backward and outward; the embedded part is curved and has a large pulp cavity.[111] The lower canine may reach a length of eight inches or more (ca. 20 cm.); the crown is prismatic and is curved backward and outward in front of the upper one, so that the friction between the two keeps a sharp edge on the lower tooth. In the sow they are much smaller.

[Illustration:

FIG. 309.—SUPERFICIAL GLANDS OF HEAD OF PIG.

_a_, Parotid gland; _a′_, _a″_, cervical and submaxillary angles of _a_; _b_, _c_, ventral and dorsal buccal glands; _d_, labial glands; _e_, masseter muscle; _f_, _f′_, lymph glands; _g_, dotted line indicating outline of submaxillary gland, which is concealed. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The average periods of =eruption= of the teeth are given in the subjoined table.

TOOTH│ ERUPTION │ CHANGE │ │ I_{1}│2 to 4 weeks │12 months I_{2}│upper 2 to 3 months│ │lower 1½ to 2 month│16 to 20 months I_{3}│Before birth │8 to 10 months C │Before birth │9 to 10 months P_{1}│5 months │ ─────┼───────────────────┼─────────────────── P_{2}│5 to 7 weeks │12 to 15 months P_{3}│upper 4 to 8 days │ „ │lower 2 to 4 weeks.│ P_{4}│upper 4 to 8 days │ „ │lower 2 to 4 weeks │ ─────┼───────────────────┼─────────────────── M_{1}│4 to 6 months │ M_{2}│8 to 12 months │ M_{3}│18 to 20 months │

The =cheek teeth= increase in size from before backward. They have (with certain exceptions noted below) complex tuberculate crowns; the term bunodont is applied to this condition, as distinguished from the selenodont structure in horses and cattle, in which there are prominent ridges of enamel. They are short-crowned teeth with a distinct neck and root. The first tooth in each jaw is small, simple, and appears only once; in the lower jaw it is near the canine, in the upper near the second cheek tooth. The next two teeth are larger, laterally compressed, and sectorial. The fourth tooth below is larger, but otherwise like the preceding ones, while the upper one is much wider and is tuberculate.

[Illustration:

FIG. 310.—DISSECTION OF MOUTH AND PHARYNGEAL REGION OF PIG.

_1_, Hard palate; _2_, tongue showing distinctly fungiform papillæ; _3_, foliate papilla; _4_, lymph nodules of soft palate; _5_, stylo-glossus muscle, out of which a portion has been cut; _6_, hyo-glossus; _7_, genio-glossus; _8_, genio-hyoideus; _9_, mylo-hyoideus (reflected); _10_, stylo-hyoideus; _11_, great cornu of hyoid bone; _12_, tensor palati; _13_, levator palati; _14_, pterygo- et palato-pharyngeus; _15_, stylo-pharyngeus; _16_, chondro-pharyngeus; _17_, sterno- et omo-hyoideus; _18_, retropharyngeal lymph glands; _a_, bulla ossea; _b_, paramastoid process. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The =parotid gland= is large and triradiate. It extends very little on to the masseter muscle and its upper angle does not quite reach the base of the ear. It is pale in color, and is embedded in fat in animals in good condition. On its deep face are several large subparotid lymph glands, some of which are only partially covered by the parotid. The =duct= arises on the deep face, has a course similar to that of the ox, and perforates the cheek opposite the fourth or fifth upper cheek tooth. Small accessory glands (Glandulæ parotideæ accessoriæ) may be found along the course of the duct.

The =submaxillary gland= is small, reddish in color, and oval in outline; it is covered by the parotid. Its superficial face is convex, and is marked by rounded prominences. From its deep face a narrow process extends forward about two or three inches (ca. 5 to 7.5 cm.) beneath the mylo-hyoideus muscle along with the duct. The latter opens near the frenum linguæ, but there is no papilla.

[Illustration:

FIG. 311.—SAGITTAL SECTION OF PHARYNGEAL REGION OF PIG, PARTLY SCHEMATIC.

_1_, Palate bone; _2_, sphenoid bone; _2′_, sphenoidal sinus; _2″_ occipital bone; _3_, epiglottis; _4_, arytenoid cartilage; _5_, thyroid cartilage; _6_, root of tongue; _7_, mouth cavity; _8_, isthmus faucium; _9_, hard palate; _10_, septum nasi; _11_, ventral muscles of head; _a_, soft palate; _a′_, free edge of _a_; _b_, dorsal wall of pharynx; _c_, fornix of pharynx; _d_, cavity of larynx; _e_, _g_, naso-pharynx; _f_, oro-pharynx; _h_, posterior pillar of soft palate; _i_, dotted line indicating lateral boundary between nasal cavity and pharynx; _k_, aditus laryngis; _l_, entrance to œsophagus; _m_, Eustachian orifice; _n_, pharyngeal recess; _o_, posterior naris. (After Ellenberger, in Leisering’s Atlas.) ]

[Illustration:

FIG. 312.—STOMACH OF PIG, PARIETAL SURFACE.

The organ contained a rather small amount of ingesta and hence is somewhat contracted. ]

[Illustration:

FIG. 313.—STOMACH OF PIG, VISCERAL SURFACE.

Organ was fixed _in situ_ and is somewhat contracted. ]

The =sublingual gland= has an arrangement similar to that of the ox. The posterior part (Glandula sublingualis grandicanalaris) is reddish-yellow in color, and is about two inches (ca. 5 cm.) long, and half an inch wide; its posterior end is in relation to the submaxillary gland and its duct. The anterior part is much larger, being two or three inches (ca. 5 to 7 cm.) long and about twice the width and thickness of the posterior part. All or most of the ducts from the posterior part unite to form the =ductus sublingualis major=, which opens near the ductus submaxillaris. Eight or ten =ductus sublinguales minores= convey the secretion from the anterior part through the floor of the mouth.

[Illustration:

FIG. 314.—DIAGRAM OF ZONES OF MUCOUS MEMBRANE OF STOMACH OF PIG. ]

[Illustration:

FIG. 315.—VISCERAL SURFACE OF STOMACH OF PIG, FROM WHICH THE SEROUS COAT HAS BEEN REMOVED. ]

[Illustration:

FIG. 316.—EVERTED STOMACH OF PIG, FROM WHICH THE MUCOUS MEMBRANE HAS BEEN REMOVED.

_O_, Œsophagus; _D_, duodenum; _Di_, diverticulum; _a_, _a′_, _a″_, _a‴_, longitudinal fibers; _b_, circular fibers; _c_, external oblique fibers; _c′_, internal oblique fibers; _c″_, cardiac loop; _d_, fibers which connect branches of cardiac loop; _f_, fold at entrance to diverticulum; _p_, pyloric sphincter; _p′_, pyloric prominence. (Ellenberger-Baum, Anat. d. Haustiere.) ]

THE PHARYNX

The =pharynx= presents in its posterior part a median cul-de-sac about an inch and a half (ca. 3 to 4 cm.) long, which is situated between the ventral straight muscles of the head and the origin of the œsophagus. Its lower margin is formed by the junction of the posterior pillars of the soft palate, which contain muscular tissue derived from the palatinus and palato-pharyngeus. The vault of the pharynx (Fornix pharyngis) is divided by a median fold of mucous membrane which is a direct continuation of the septum nasi. On either side of this is an infundibulum in which the Eustachian tube opens.

THE ŒSOPHAGUS

The =œsophagus= is short and nearly straight. It has (according to Rubeli) a potential caliber of nearly 3 inches (ca. 7 cm.) at either end, and about 1⁷⁄₁₀ inches (ca. 4.2 cm.) in its middle part.[112] The muscular coat, except near the cardia, is striated. There are mucous glands in the submucosa to about the middle of the tube.

[Illustration:

FIG. 317.—ABDOMINAL VISCERA OF YOUNG PIG, VENTRAL ASPECT.

The stomach was very large in this subject. ]

[Illustration:

FIG. 318.—DIAGRAM OF CÆCUM AND COLON OF PIG.

Coils of colon have been pulled apart somewhat. ]

[Illustration:

FIG. 319.—SOLITARY NODULES FROM LARGE INTESTINE OF PIG. (Ellenberger-Baum, Anat. d. Haustiere.) ]

[Illustration:

FIG. 320.—ILEO-CÆCAL OPENING AND ADJACENT PART OF CÆCUM AND COLON OF PIG.

_a_, Mucous membrane of colon; _b_, mucous membrane of cæcum; _c_, Peyer’s patch; _d_, ileo-cæcal opening; _e_, end of ileum; _f_, folds (frenula) of ileum. (After P. Schumann.) ]

THE STOMACH

The =stomach= is large and pyriform. Its average capacity is about 1½ to 2 gallons (ca. 5.7 to 8 liters). When full it extends backward to the last left intercostal space laterally and the umbilicus ventrally. The left portion is large and rounded, while the right portion (Pars pylorica) is small, and bends sharply upward to join the small intestine. The parietal surface is related to the liver, gall-bladder, and diaphragm. The visceral surface is related to the intestine, the mesentery, and the pancreas. The great curvature is related to the diaphragm, spleen, and abdominal floor. The pyloric end lies on the right lateral lobe of the liver. The left extremity presents a flattened conical blind pouch, the =diverticulum ventriculi=, the apex of which projects backward. The œsophagus joins the stomach very obliquely, almost in the median plane, and about three or four inches (ca. 8 to 10 cm.) below the twelfth thoracic vertebra. The cardiac opening is slit-like and is bounded above and to the left by a fold which contains a thickening of the internal oblique layer of the muscular coat. The opening into the diverticulum is situated above and a little to the left of the cardia; it is transversely oval, and is bounded (except externally) by a thick fold which contains spirally arranged muscular fibers. The mucous membrane may be divided into four regions. Over a quadrilateral area around the cardia (about one inch on the right and two or three inches on the left side of the orifice) it is œsophageal in character, and presents a number of folds. A sharp line of demarcation separates this from the rest of the mucous membrane, which is soft and glandular. The second or cardiac gland region is pale gray in color and thin (ca. 0.5 to 1 mm.); it extends about to the middle of the stomach. The third or fundus gland region is readily distinguished by its thickness (ca. 3 mm.) and its brownish-red mottled appearance.[113] The fourth or pyloric region is pale, thinner than the preceding, and presents a number of irregular folds. At the pylorus there is a remarkable ridge which projects from the wall of the lesser curvature and diminishes considerably the size of the orifice. It is about an inch and a half (ca. 3 to 4 cm.) long and nearly half an inch (ca. 1 cm.) high. Sometimes it is grooved; in other cases it has the form of a rounded eminence attached by a pedicle to the wall. Fibers from the circular muscular coat extend into it.

[Illustration:

FIG. 321.—LIVER OF PIG, SOFT SPECIMEN SKETCHED WITH LOBES DRAWN APART. ]

THE INTESTINE

The =small intestine= is 50 to 65 feet (ca. 15 to 20 m.) long. The mesentery of about the first two feet (ca. 60 cm.) is two to two and a half inches (ca. 5 to 6 cm.) long; this part may be termed duodenum. The remainder (Jejuno-ileum) has a mesentery about six to eight inches (ca. 15 to 20 cm.) long, which is thick and contains a quantity of fat, and numerous large lymph glands at its root; the root is attached in the sublumbar region behind the stomach and blends here with the mesentery of the large intestine. The small intestine is arranged in close coils and lies mainly on the left side and floor of the abdomen, from the stomach to the pelvis; some coils, however, lie against the right flank. The opening of the =bile-duct= is about one or two inches (ca. 2.5 to 5 cm.) from the pylorus, and that of the =pancreatic duct= about four or five inches (ca. 10 to 15 cm.) beyond it. =Peyer’s patches= and =solitary glands= are numerous and very distinct; the patches are usually band-like and prominent; the solitary glands form projecting nodules marked by crypts.

[Illustration:

FIG. 322.—LIVER OF PIG, VISCERAL SURFACE.

Photograph of specimen hardened _in situ_. ]

The =large intestine= is about 15 feet (ca. 4 to 5 meters) in length, and is for the most part much wider than the small intestine; it is connected by a mesentery with the dorsal abdominal wall between the kidneys. The =cæcum= is cylindrical, about 8 to 12 inches (ca. 20 to 30 cm.) long, and 3 to 4 inches (ca. 8 to 10 cm.) wide. It lies against the upper part of the right flank, its blind end reaching to within about two inches (ca. 5 cm.) of the pelvic inlet. The ileum joins the cæcum obliquely and projects somewhat into its lumen. The =colon= has at first about the same caliber as the cæcum, but becomes gradually smaller. Most of it is arranged in three close, double spiral coils in the mesentery, in relation chiefly to the right flank externally, and to the small intestine behind and to the left. On emerging from this spiral labyrinth, it passes forward to the stomach and pancreas and then turns backward; this terminal part is narrow, median in position, and closely attached by a short mesentery to the sublumbar region. The =rectum= is usually surrounded by a quantity of fat. The cæcum has three longitudinal muscular bands and three rows of sacculations, which are continued a short distance on the colon. The spiral colon has two bands and two series of sacculations, which, however, gradually disappear in the centrifugal part.

THE LIVER

[Illustration:

FIG. 323.—LIVER OF PIG, PARIETAL SURFACE.

Photograph of specimen hardened _in situ_. ]

The liver is relatively large, its average weight being about 4 to 4½ pounds (ca. 2 kg.). It is thick and very strongly curved.[114] It is divided by three deep interlobar incisures into four principal =lobes=—=right lateral=, =right central=, =left central=, =left lateral=; the last of these is usually considerably the largest. On the upper part of the right lateral lobe is the =caudate lobe= and its process. That part of the right central lobe which lies below the portal fissure and to the left of the gall-bladder and cystic duct is homologous with the quadrate lobe of man. The parietal surface is extremely convex, its most anterior part reaching to a plane through the lower part of the sixth or seventh intercostal space. The visceral surface is deeply concave; most of it is related to the stomach, for which there is a correspondingly large and deep gastric impression. There is a duodenal impression on the upper part of the right lateral lobe, but no renal impression, as the right kidney does not touch the liver. The fossa for the gall-bladder is mainly on the right central lobe, but also in part on the adjacent surface of the left central lobe. The posterior vena cava enters the dorsal border of the caudate lobe and soon becomes entirely embedded in the gland substance, emerging only at its passage through the diaphragm. The œsophageal notch is large and is occupied mainly by the large right crus of the diaphragm. The right lateral border extends backward to the upper part of the twelfth intercostal space or thirteenth rib. The left lateral border is opposite the eighth rib and intercostal space. The ventral border extends backward about as far as the umbilicus.

There are no lateral ligaments and the falciform ligament disappears early.

The =gall-bladder= is attached in the fossa vesicæ felleæ on the right central lobe, at a considerable distance from the ventral border. The cystic duct joins the hepatic duct at an acute angle immediately after the emergence of the latter from the portal fissure. The =bile-duct= (Ductus choledochus) opens at the papilla duodeni about one or two inches (ca. 2.5 to 5 cm.) from the pylorus.

[Illustration:

FIG. 324.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, LEFT SIDE.

_D_, Costal line of diaphragm; _U_, ureter; _V. S._, vesicula seminalis; _B. g._, bulbo-urethral gland; _P_, penis. ]

[Illustration:

FIG. 325.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, RIGHT SIDE.

_D_, Costal attachment of diaphragm; _O_, ovary. ]

Owing to the large amount of interlobular tissue, the =lobules= are mapped out sharply; they are polyhedral in form and are 1 to 2.5 mm. in diameter. For the same reason the gland tissue is much less friable than that of the other animals, from which it is easily distinguished.

THE PANCREAS

The =pancreas= is elongated, and is situated transversely on the dorsal abdominal wall, with its right extremity on the ventral surface of the right kidney, and the left end touching the dorsal end of the spleen and the left kidney. The right portion has two lobes; the posterior lobe bends around the great mesenteric artery and the portal vein; the anterior one is pointed, extends downward and forward about in the median plane, and is attached to the portal fissure and the duodenum. The left portion is prismatic and rests mainly on the left sac of the stomach, its left extremity being included between the left kidney and the dorsal end of the spleen. The pancreatic =duct= passes from the anterior lobe directly through the duodenal wall, opening about five or six inches (ca. 12.5 to 15 cm.) from the pylorus. The interlobular tissue usually contains a good deal of fat.

THE SPLEEN

The =spleen= is long and narrow. Its long axis is nearly dorso-ventral in direction, and is slightly curved to conform to the left part of the greater curvature of the stomach. The dorsal end lies under the vertebral ends of the last three ribs. The ventral end is smaller, reaches to the ventral abdominal wall, and lies against the left lobe of the liver. The visceral surface has a longitudinal ridge on which the hilus is situated; this divides the surface into nearly equal gastric and intestinal areas. The spleen is attached so loosely to the stomach that it may be regarded as being intercalated in the great omentum. In large subjects it may reach a length of 15 to 18 inches (ca. 38 to 45 cm.) and a width of 3 to 4 inches (ca. 8 to 10 cm.).

DIGESTIVE SYSTEM OF THE DOG

THE MOUTH

The size and form of the mouth vary greatly in different breeds, the cavity being in some long and narrow, in others short and wide. The =rima oris= is very extensive, so that the labial commissure is opposite the third or fourth cheek tooth. The =lips= are thin and mobile, and present numerous tactile hairs. The upper lip has a small, central, bare area which forms part of the muzzle, and is marked by a central groove, the philtrum, or (as in the bulldog) a fissure, giving the appearance of harelip. The lateral borders of the lower lip are flaccid and denticulated. The mucous membrane is usually pigmented and forms distinct frena labiorum. The labial glands are small and scanty.

[Illustration:

FIG. 326.—TONGUE OF DOG. _a_, Tonsil; _b_, vallate papillæ; _c_, foliate papilla; _d_, fungiform papillæ; _e_, median groove of dorsum; _f_, epiglottis; _g_, soft papillæ of root; _h_, middle glosso-epiglottic fold; _1_, tip; _2_, root. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The =cheeks= are loose and capacious, and their mucous lining is smooth and more or less pigmented. The =parotid duct= opens usually opposite the third upper cheek tooth. Near the last tooth are the openings of the four or five ducts from the orbital gland.

The =hard palate= is widest between the fourth pair of cheek teeth. It has eight to ten curved ridges on either side of the raphé. Behind the first pair of incisor teeth is the triangular incisive papilla, at which the naso-palatine ducts open. The mucous membrane is usually pigmented.

The =soft palate= is thick except at its margins. In the resting state of the parts it comes in contact with the oral surface of the epiglottis. Between its anterior and posterior pillars on either side is a marked tonsillar sinus, in which an elongated =tonsil= is situated; this is reddish in color, about an inch long, and projects somewhat into the fauces between two folds of mucous membrane.