Page 400 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Digestive System / 385

entirely fills the left side of the abdominal the ox makes contact with the right body
wall. The omasum of the sheep and goat is
cavity; its capacity depends on the size of
VetBooks.ir the individual but in adult cattle ranges much smaller than the bovine omasum and
normally is not in contact with the abdomi­
from 110 to 235 L (about 30 to 60 gallons).
The rumen is subdivided internally into nal wall. Food enters the omasum at the
compartments by muscular pillars, which reticulo‐omasal orifice, between the laminae,
correspond to grooves visible on the exte­ and goes on to the omasoabomasal orifice.
rior of the rumen (Figs. 20‐13 and 20‐14).
Right and left longitudinal pillars (corre­ Abomasum
sponding to right and left longitudinal
grooves on the exterior) together with cra- The abomasum (true stomach) is the first
nial and caudal pillars (externally, cranial glandular portion of the ruminant digestive
and caudal grooves) form a nearly com­ system (Figs. 20‐13 and 20‐14). Its proximal
plete constricting circle in the horizontal portion is ventral to the omasum, and its
plane. These divide the rumen into dorsal body extends caudad on the right side of
and ventral sacs. The dorsal sac is the larg­ the rumen. The pylorus demarcates the
est compartment. The dorsal sac is con­ muscular junction of the stomach and small
tinuous cranially with the reticulum over intestine, and like the porcine pylorus, it
the ruminoreticular fold so that the two features an enlarged torus pyloricus.
compartments share a dorsal space. The epithelium of the abomasum con­
Caudally, the dorsal sac is further subdi­
vided by the dorsal coronary pillars, which sists primarily of two glandular regions,
equivalent to the fundic gland region
form an incomplete circle bounding the (region of the proper gastric glands) and
dorsal blind sac. The caudal part of the ven­ the pyloric gland region. The cardiac gland
tral sac forms a diverticulum, the ventral region in the abomasum is confined to a
blind sac, separated from the rest of the very small area adjacent to the omasoabo­
ventral sac by the ventral coronary pillars. masal orifice.
As in the rest of the forestomach, the
mucous membrane lining the rumen is a non­
glandular, stratified squamous epithelium. Small Intestine
The most ventral parts of both sacs of the
rumen contain numerous feathery papillae up The duodenum is the first of three divi­
to 1 cm long, but papillae are almost entirely sions of the small intestine (Figs. 20‐15 to
absent on the dorsal part of the rumen. 20‐17). It is closely attached to the right
side of the dorsal body wall by a short
mesentery, the mesoduodenum. The duo­
Omasum denum arises at the pylorus of the stomach
and receives ducts from the pancreas and
The omasum is a spherical organ filled liver in this region. In all species it passes
with muscular laminae (an estimated 90 to caudad on the right side of the abdominal
130 in the bovine omasum) that lie in cavity toward the pelvic inlet, then crosses
sheets, much like the pages of a book (giv­ to the left side caudal to the root of the
ing the omasum its colloquial name, book great mesentery (discussed later) and
stomach). The stratified squamous mucous reflects craniad to join the jejunum. The
membrane covering the laminae is studded duodenum is attached at this site to
with short, blunt papillae. Each lamina the descending colon by a serosal ligament,
contains three layers of muscle, including a the duodenocolic fold.
central layer continuous with the tunica The transition between duodenum and
muscularis of the omasal wall. the next portion of the small intestine, the
The omasum lies to the right of the rumi­ jejunum, is defined by the marked increase
noreticulum, just caudal to the liver, and in in the length of the supporting mesentery.