460 



DIGESTIVE SYSTEM OF THE OX 



omasicum) is situated in the medial wall of the reticulum, about five or six mches 

 above the bottom of the latter. It is rounded, and is limite^ below and laterally 

 by the junction of the lips of the oesophageal groove. 



The cavity of the omasum is occupied to a considerable extent by about a 

 hundred longitudinal folds, the laminae omasi, which spring from the dorsal wall 

 and the sides. The largest of thest^a dozen or more in number— have a convex 

 attached edge, and a ventral, concave free edge, which reaches to within a short 

 distance of the ventral wall of the sac. If these are drawn apart or a cross- 

 section is made (Fig. 392), it will be seen that there is a second order of shorter 

 laminsfi, and a third or fourth still shorter; finally there is a series of very low folds 

 or lines. The food is pressed into thin layers in the narrow spaces between the 

 laminaj (Recessus interlaminares) , and reduced to a fine state of division by bemg 

 ground doAvn lay the numerous rounded, horny papillee which stud the surfaces of 

 the folds. The ventral wall of the omasum forms a groove, the sulcus omasi, 



which connects the reticulo- 

 omasal opening with the 

 omaso-abomasal opening; it is 

 about three inches (ca. 7-8 

 cm.) long, and is directed back- 

 ward and downward. It is 

 free from laminae, but presents 

 usually slight folds and small 

 papilte; it may function ' as a 

 direct path from the reticulum 

 to the abomasum for fluid and 

 finely divided food. In the 

 neck of the omasum there are 

 thick folds, and a number of 

 the peculiar papillfe already 

 mentioned as occurring in the 

 lower part of the oesophageal 

 groove. The omaso-abomasal 

 orifice (Ostium omaso-abo- 

 masicum) is oval, and is about 

 four inches (ca. 10 cm.) long. 

 It is bounded in front by a 

 thick muscular pillar, the fibers 

 of which spread out above in 

 the sides of the omasum. The 

 mucous membrane forms an 

 extensive fold on each side of the opening; these folds may act as valves (Valvulae 

 terminales), which probably prevent regurgitation of the contents of the abomasum. 

 The cavity of the abomasum is divided by a constriction into two areas. The 

 first of these (fundus gland region) is lined with a soft glandular mucous membrane, 

 which forms a dozen or more extensive spiral folds (Plicae spirales) . The second 

 part (pyloric region) is much narrower and resembles in appearance the corre- 

 sponding region of the horse's stomach. A small cardiac gland zone surrounds the 

 omaso-abomasal orifice. The pyloric orifice is small and round. 



Structure. — The serous coat invests all of the free surface of the stomach. 

 The surface of the rumen which is attached to the dorsal abdominal wall is, of 

 course, uncovered, as well as the adjacent area to which the spleen is attached. 

 The furrows are bridged over by the peritoneum and superficial muscle-fibers, 

 and contain fat and (in most cases) branches of the gastric arteries. 



The lesser omentum passes from the visceral surface of the liver to the right 



Fig. 392. — Cross-sectiox of Omasum of Ox. 

 1-5, Lamiuse of various orders; 6, neck connecting with reticulum. 



