1054 THE DIGESTIVE SYSTEM. 
and hangs down in front of the intestines to a variable extent. When the abdomen 
is carefully opened without disturbing the viscera, it is rare to find the great 
omentum evenly spread over the front of the intestines. More commonly it is folded 
in between some of the coils of intestine, or tucked into the left hypochondrium ; 
or perhaps it is carried upwards in front of the stomach by a distended transverse 
colon. It extends between the great curvature of the stomach above and the 
transverse colon below, not taking the shortest course from one of these to the other, 
but hanging down as a loose fold between the two. The lower part of the small 
sac is continued down within it (Fig. 707). 
The great omentum may be said to consist of two folds, each formed of two 
layers, one derived from each sac of the peritoneum. The anterior or descending fold 
begins at the great curvature of the stomach, where it is formed by the meeting of 
the two layers from the superior and inferior surfaces of that organ respectively ; 
from this it descends to the lower border of the omentum, where, turning back 
upon itself (Fig. 707), it passes up as the posterior or ascending fold. This runs 
upwards until it meets the transverse colon; here its two layers separate to enclose 
and cover that colon—and the omentum properly so called ceases. Its two layers, 
however, unite at the upper surface of the colon (Fig. 707) to form the transverse 
mesocolon, which is continued upwards and backwards to the anterior border of the 
pancreas. Here the layers of the transverse mesocolon again separate—the upper, 
derived from the small sac, running backwards and upwards over the upper surface 
of the pancreas to the posterior abdominal wall; the lower, derived from the great 
sac, passing downwards along the back of the abdomen, as already explained. 
The great omentum is continued to the right for a short distance (25 mm.) along the lower border 
of the duodenum. At the left end it shortens very much, and is directly continued into the 
gastro-splenie omentum ; the spleen, as it were, being introduced between the two layers instead 
of the colon. 
Functions of the Great Omentum.—Numerous uses have been assigned to the great 
omentum ; the chief seem to be: (1) To act as a movable packing material, capable of filling all 
temporarily-produced spaces in the abdomen. (2) It probably, to some extent, prevents the pas- 
sage of the small intestine up into the stomach chamber, and helps to keep them from getting 
entangled there. (3) It is a storehouse of fat. (4) It is said to be “the great protector against 
peritoneal infectious invasions.” Being freely movable, it can pass to almost any part of the 
abdomen, and there “ build up barriers of exudations to check infection ” (Byron Robinson). 
Mr. Lockwood has made the interesting observation (in connexion with the contents of hernie) 
that, in bodies under forty-five years of age, the omentum can rarely be drawn down below the 
level of the pubic spine ; in older bodies the reverse is the rule. 
The gastro-splenic omentum is a short fold composed of two layers, the anterior 
or ore superficial being derived from the great sac, the posterior or deeper from the 
small sac (Fig. 709, A). It is attached by one margin to the wide end of the stomach 
(just below the line of the great curvature), and by the other to the gastric surface 
of the spleen just in front of the hilus. Between its two layers the vasa brevia of 
the splenic artery pass from the spleen to the stomach. Below and in front, its 
layers are continued into the corresponding layers of the great omentum; above 
and behind, they separate at the “uncovered area ” of the stomach (Fig. 710). 
Minor Folds of Peritoneum.—The phreno-colic ligament, passing from the 
splenic flexure of the colon to the diaphragm opposite the 10th or 11th ribs, has been 
deseribed in connexion with the splenic flexure. The mesentery of the appendix, and 
the folds and fosse around the ileo-cxeeal region, are included in the account of the 
cxecum, as are those around the duodenum in the description of that viscus. “The 
lieno-renal and hepato-renal ligaments have been referred to incidentally above. 
DEVELOPMENT OF THE INTESTINAL CANAL AND PERITONEUM. 
As already explained on p. 31, when the embryo begins to take definite shape, and to 
be marked off from the general surface of the blastodermic vesicle by an infolding of its 
margins—resulting in the formation of the cephalic or head fold, the caudal or tail fold, 
and the lateral folds—a portion of the cavity of the vesicle is cut off by these folds, and 
more or less completely enclosed within the body of the embryo, to form the primitive 
alimentary canal. This is simply an imperfect tubular cavity, situated beneath the 
