300 THE ANATOMY OF THE HORSE. 



parietes ; but, at otlier times, the connection between the parietal and 

 visceral peritoneum is traceable along bands or folds analogous to the 

 sling-like membrane that was formed in the imaginary case. These 

 folds constitute the various mesenteries, omenta, and peritoneal liga- 

 ments that will hereafter be described. 



Although there is but a single peritoneal sac, this sac is so disposed 

 that it forms two compartments, termed respectively the greater and 

 lesser cavities of the peritoneum, the latter being also known as the 

 cavity of Winslow. The greater cavity is that which is exposed when 

 the inferior wall of the abdomen is removed, the lesser cavity is situated 

 behind the stomach, and is separated from the greater cavity mainly by 

 the omentum. 



The Great or Gastro-colic Omentum. — Passing backwards among the 

 intestines, on the left side of the abdomen, there will have been noticed 

 a large lace-like membrane, which is the fjreat omentum^ epiiilorm, or web. 

 In order to examine its connection, the caecum and double colon should 

 be thrown backwards over tlie right flank, and the coils of the single 

 colon arranged over the left flank. The coils of small intestine should 

 at the same time be gathered backwards and to the right. The omen- 

 tum is composed of two layers of peritoneum, Avhich include between 

 them vessels, and a vaiying quantity of fat. This fat is deposited 

 mainly along the course of the vessels, leaving, except in obese subjects, 

 inters'eniug transparent areas that are free from fat ; and it is from this 

 arrangement that the membrane possesses a lace-like appearance. The 

 two layers of the omentum may be distinguished as superficial and 

 deep. 



When the superficial layer is traced backwards, it is seen to pass on 

 to the terminal part of the double colon (4th part) and initial part oi' 

 the single colon, covering the posterior aspect of these where they extend 

 across the roof of the abdominal cavity. Behind these it passes back- 

 wards along the roof of the abdominal cavity, from which it descends to 

 envelop the small intestine, forming the great mesentery, and the float- 

 ing colon, forming the colic mesentery. To the right, again, it passes 

 directly on to the caicum and the double colon ; and after enveloping 

 these intestines, it returns to the abdominal wall, to pursue its back- 

 ward course to the pelvis. When followed forwards, the superficial 

 layer reaches the convex curvature of the stomach, and the initial dila- 

 tation of the duodenum; and it passes over the anterior surfaces of 

 these organs as visceral peritoneum. Passing off" the duodenum and 

 stomach, it next forms the anterior layer of the gastro-hepatic omen- 

 tum, and thus reaches the posterior surface of the liver at the portal 

 fissure. From tliat point it descends over the posterior surface of the 

 liver as visceral peritoneum, and turns round the inferior edge of the 

 gland to gain its diaphragmatic surface. It ascends on this surface ; 



