460 DIGESTIVE SYSTEM OF THE OX 
omasicum) is situated in the medial wall of the reticulum, about five or six inches 
above the bottom of the latter. It is rounded, and is limited below and laterally 
by the junction of the lips of the asophageal groove. 
The cavity of the omasum is occupied to a considerable extent by about a 
hundred longitudinal folds, the lamingz omasi, which spring from the dorsal wall 
and the sides. The largest of these—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 
lamine, and a third and 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 
laminze (Recessus interlaminares), and reduced to a fine state of division by being 
ground down by the numerous rounded, horny papillsee 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 lamin, but presents 
usually sight folds and small 
papillze; 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 papille already 
mentioned as occurring in the 
lower part of the cesophageal 
groove. The omaso-abomasal 
orifice (Ostium omaso-abo- 
masicum) is oval, and is about 
four inches (ca. 10 em.) long. 
It is bounded in front by a 
thick muscular pillar, the fibers 
Fic. 392.—Cross-secTion or Omasum or Ox. of which spread out above in 
1-5, Laminsx of various orders; 6, neck connecting with reticulum. the sides of the omasum The | 
mucous membrane forms an | 
extensive fold on each side of the opening; these folds may act as valves (Valvule 
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 (Plicxe 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 
