THE PELVIC CAVITY THE STOMACH 453 



ribs, or through the last thoracic vertebra. . The chief differential features in the 

 arrangement of the peritoneum will be described with the viscera. The sub- 

 peritoneal tissue is more abundant than in the horse, and in general contains a 

 much larger amount of fat. 



THE PELVIC CAVITY 



The pelvic cavity is relatively long and narrow. The inlet is more oblique 

 than that of the horse; it is elliptical in outline, and the transverse diameter is 

 smaller than that of the horse. The pubic part of the floor is about horizontal, 

 but the ischiatic part slopes dorsally to a marked degree; this part is also deeply 

 concave transversely. The roof is concave in both directions. The peritoneum 

 extends backward as far as the first coccygeal vertebra, so that the retroperitoneal 

 part of the cavity is short. 



THE STOMACH 



General Arrangement. — The stomach of the ox is very large, and occuoies 

 nearly three-fourths of the abdominal cavity. It fills the left half of the cavity 

 (with the exception of the small space occupied by the spleen) and extends con- 

 siderably over the median plane into the right half. 



It is compound, and consists of four divisions, viz., rumen, reticulum, omasum, 

 and abomasum.i The division is clearly indicated externally by furrows or con- 

 strictions. The first three divisions are often regarded as proventriculi or ceso- 

 phageal sacculations, the fourth being the stomach proper (in the narrower sense 

 of the term). The oesophagus opens into the stomach on a sort of dome, the 

 atrium ventricuU, and is continued through the reticulum by the oesophageal 

 groove. From the ventral end of the latter a groove traverses the ventral wall of 

 the omasum, thus giving a direct path from the reticulum to the abomasum for 

 finely divided food or fluid. The abomasum joins the small intestine. 



Capacity. — ^The capacity of the stomach varies greatly, depending on the age ' 

 and size of the animal. In cattle of medium size it holds 30 to 40 gallons, in large 

 animals 40 to 60, in small, 25 to 35. The relative sizes of the four parts vary with 

 age, in correlation with the nature of the food. In the new-born calf the rumen and 

 reticulum together are about half as large as the abomasum; in ten or twelve weeks 

 this ratio is reversed. During this period the omasum appears to be contracted 

 and functionless. At four months the rumen and reticulum together are about 

 four times as large as the omasum and abomasum together. At about one and one- 

 half years the omasum equals or approaches closely the abomasum in capacity. 

 The four divisions have now reached their definitive relative capacities, the rumen 

 constituting about 80 per cent., the reticulum 5 per cent., the omasum 7 or 8 per 

 cent., and the abomasum 8 or 7 per cent, of the total amount. 



Exterior and Relations 



The rumen occupies almost all of the left half of the abdominal cavity, and 

 extends considerably over the median plane ventrally and in its middle. It is 

 somewhat compressed from side to side and may be described as having two sur- 

 faces, two curvatures or borders, and two extremities. The parietal (or left) 

 surface (Facies parietalis ) is convex and is related to the diaphragm, left wall of 

 the abdomen, and spleen. It extends from the ventral part of the seventh inter- 

 costal space almost to the pelvis. The visceral (or right) surface (Facies visceralis) 

 is somewhat irregular, and is related chiefly to the omasum and abomasum, the 



^ In popular language these are regarded as so many stomachs, and are often designated 

 numerically. Other names are in common use, e. g., paunch, honeycomb, manifold or manyplies, 

 and rennet or true stomach. 



