1242 THE DIGESTIVE SYSTEM. 



between the spleen and stomach. The greater omentum is thus commonly 

 described as extending between the greater 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, and containing 

 between the anterior and posterior folds a cavity continuous with the omental 

 bursa (Fig. 968). 



This is the condition in the embryo, but in the adult the anterior fold usually 

 becomes adherent to the colon, and, below it, also to the posterior fold, and hence 

 the cavity becomes largely obliterated. If the gastro-colic ligament be included as 

 part of the greater omentum, and the embryonic condition is retained, as is usually 

 described in English text-books, the greater 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 greater curvature of the stomach, where it is 

 formed by the meeting of the two layers from the anterior and posterior surfaces 

 of that organ respectively ; from there it descends to the front of the transverse 

 colon. Leaving the colon, or passing anterior to it, see Fig. 964, the two layers 

 proceed to the lower border of the omentum, where, turning back (Fig. 964), they 

 pass up as the posterior or ascending fold. That runs upwards until it meets the 

 transverse colon ; there its two layers separate to enclose and cover that colon and 

 the greater omentum, properly so called, ceases. Its two layers, however, unite at 

 the superior margin of the colon (Fig. 964) to form the transverse mesocolon, which 

 is continued upwards and posteriorly to the anterior border of the pancreas. There 

 the layers of the transverse mesocolon again separate the superior running up- 

 wards over the anterior surface of the pancreas to the posterior abdominal wall 

 and lining the omental bursa ; the lower passing downwards on the posterior 

 abdominal wall, as already explained. 



The greater omentum is continued to the right for a short distance (25 mm.) along the inferior 

 border of the duodenum. At the left end it shortens very much, and is directly continued into 

 the gastro-lienal ligament; the spleen, as it were, being introduced between the two layers 

 instead of the colon. 



Functions of the Greater Omentum. Numerous uses have been assigned to the great 

 omentum ; the chief seem to be : (1) To act as a movable and easily adjustable packing material, 

 capable of filling all temporarily-produced spaces in the abdomen. In this respect it may be 

 compared with the Haversian fatty pads in joints. (2) It probably, to some extent, prevents the 

 passage of the small intestines 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." 



Mr. Lockwood has made the interesting observation (in connexion with the contents of herniae) 

 that, in bodies under forty- five years of age, the omentum can rarely be drawn down below the 

 level of the pubic tubercle ; in older bodies the reverse is the rule. 



The gastro-lienal ligament is a short fold composed of two layers an anterior, 

 lining the general peritoneal sac, and a posterior, lining the omental bursa (Fig. 966). 

 It is attached by one margin to the fundus and greater curvature of the stomach, 

 and by the other to the gastric surface of the spleen just in front of the hilum. 

 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 correspond- 

 ing layers of the gastro-colic ligament; above and behind, they separate at the 

 "uncovered area" of the stomach (Fig. 969). 



Minor Folds of Peritoneum. The phrenico-colic ligament, passing from the left 

 flexure of the colon to the diaphragm opposite the 10th or llth ribs, has been 

 described, and also the mesentery of the vermiform process, the lieno-renal and 

 hepato-renal ligaments. 



DEVELOPMENT OF THE DIGESTIVE SYSTEM. 



In the section on General Embryology it has been pointed out that the alimentary 

 canal is formed from three separate parts. (1) A middle large entodermal portion, and 

 (2) two smaller ectodermal parts, one anterior, the oral sinus or stomodseum, and one 

 posterior, the proctodseum. 



