Part 138

The fornix is narrow. The orifices of the Eustachian tubes are small and slit-like; the end of the tube causes a rounded projection of the mucous membrane (Torus tubarius). The œsophageal opening is relatively small and is encircled by a fold of the mucous membrane. The hyo-pharyngeus muscle is clearly divided into a kerato-pharyngeus and a chondro-pharyngeus.

THE ŒSOPHAGUS

The =œsophagus= is relatively wide and dilatable except at its origin. The constriction at its origin is termed the =isthmus œsophagi=. The cardiac end is slightly dilated; it joins the stomach under the tenth or eleventh thoracic vertebra, slightly to the left of the median plane. The muscular tissue is striated and consists mainly of two layers of spiral fibers which cross each other; near the cardia, however, the fibers are longitudinal and circular. There are mucous glands and lymph glands in the submucosa throughout.

FIG. 331.—STOMACH OF DOG. PARIETAL SURFACE.

Organ fixed in situ when well filled. ]

THE STOMACH

The =stomach= is relatively large. Its capacity in a dog weighing about 40 pounds is about six to seven pints.

Colin estimates the average capacity at about 3 liters (ca. 6½ pints), with a range between 0.6 and 8 liters (ca. 1⅓ to 17½ pints). Neumayer gives the capacity as 100 to 250 c.c. per kilogram of body-weight (ca. 2.7 ounces per pound). The average capacity of the human stomach is estimated at 35 to 40 ounces—only about one-half of that of a dog of medium size.

When full it is irregularly pyriform. The left or cardiac part (Corpus ventriculi) is large and rounded, while the right or pyloric part (Pars pylorica) is small and cylindrical. When empty, or nearly so, the left sac is strongly contracted; the pyloric part is not materially affected by variations in the amount of ingesta.

The parietal surface of the full stomach is very extensive, strongly convex, and faces partly forward, but largely to the left. It is related to the liver, the left part of the diaphragm, and the left and ventral abdominal wall as far back as a transverse section through the second or third lumbar vertebra.

The visceral surface is much less extensive and is considerably flattened; it faces chiefly to the right, and is related to the intestine, pancreas, and left kidney.

The upper part of the lesser curvature is nearly straight and vertical, but the lower part forms a deep, narrow angle, due to the fact that the pyloric part is directed sharply forward and upward.

The greater curvature is nearly four times as long as the lesser curvature. In the full stomach it extends considerably behind the left costal arch (having carried the spleen backward); ventrally, it lies on the abdominal wall, almost midway from the xiphoid cartilage to the pubis.

FIG. 332.—STOMACH OF DOG, VISCERAL SURFACE.

Organ fixed in situ when well filled. ]

The left extremity or fundus is large and rounded; it is the most dorsal part of the organ, and lies under the dorsal ends of the eleventh and twelfth ribs.

The pyloric extremity is small and is directed forward and somewhat upward; it lies usually about an inch or two (ca. 3.5 to 5 cm.) below the cardia, a little to the right of the median plane. It is related to the portal fissure of the liver and to the pancreas.

FIG. 333.—EVERTED STOMACH OF DOG FROM WHICH THE MUCOUS MEMBRANE IS REMOVED.

O, Œsophagus; D, duodenum; b, circular fibers; c′, internal oblique fibers; c″, cardiac loop; c‴, transition of internal to external oblique fibers; d, fibers uniting branches of cardiac loop; p, pyloric sphincter; p′, antral sphincter. (Ellenberger-Baum, Anat. d. Haustiere.) ]

FIG. 334.—DIAGRAM OF ZONES OF MUCOUS MEMBRANE OF STOMACH OF DOG. ]

The cardia is situated about two to three inches (ca. 5 to 7 cm.) from the left extremity, and is oval; it lies a little to the left of the median plane, below the tenth or eleventh thoracic vertebra.

When empty, or nearly so, the stomach is separated from the ventral abdominal wall by the liver and small intestine, and the greater curvature extends back to the eleventh or twelfth rib. In this state there is not rarely a marked constriction between the right and left portions.

The longitudinal muscular fibers are found on the curvatures and on the pyloric part. The oblique fibers are arranged in two layers: the external layer is a continuation of the longitudinal fibers of the œsophagus onto the body and fundus. The circular layer covers the whole stomach except the fundus, and forms a pyloric sphincter and an antral sphincter. The internal oblique layer is arranged as in the horse, and forms a similar loop-like, cardiac sphincter.

Three regions of the mucous membrane exist. Cardiac glands are found in a very narrow pale zone around the cardiac opening, and also scattered along the lesser curvature. The fundus gland region has a thick, reddish-brown mucous membrane, which lines about two-thirds of the organ. The pyloric mucous membrane is thinner and pale; in the dead subject it is often stained by regurgitated bile.

FIG. 335.—ABDOMINAL VISCERA OF DOG.

Superficial ventral view after removal of the great omentum. From photograph of formalin-hardened subject. ]

THE INTESTINE

The intestine is short—about five or six times the length of the body.