302 THE ANATOMY OF THE HORSE. 



forefinger towards the right, above and behind the pylorus. The tips of 

 the forefingers of opposite hands can thus be made to meet, showing the 

 continuity of the larger sac of the peritoneum, in which the left hand is, 

 with the smaller sac, or cavity of Winslow, in which the right hand is. 

 Perhaps the simplest way to get an understanding of the relationship of 

 the two cavities, is to imagine the deep layer of the omentum to be 

 suppressed. In that condition, the anterior aspect of the double and 

 single colon at their point of junction, the pancreas, the posterior 

 surface of the stomach and initial dilatation of the duodenum, the upper 

 parts of the liver and diaphragm, and the roof of the abdomen for a 

 short space behind the hiatus aorticus would be without a serous cover- 

 ing. It may be supposed that to supply this deficiency, a pouch of the 

 great sac of peritoneum has to be made. This pouch is made at the 

 foramen of Winslow, the peritoneum being there thrust outwards 

 towards the right, and expanded until it forms what has already been 

 traced as the deep layer of the omentum. The foramen will be observed 

 to have the following boundaries : — the base of the lobulus caudatus iu 

 front, the 4th part of the double colon behind, the free edge of the 

 gastro-hepatic omentum below, and the posterior vena cava and right 

 pillar of the diaphragm above. 



The Great Mesentery is the membrane that suspends the small intes- 

 tine. Like the omentum, it is composed of two layers of peritoneum. 

 These layers leave the spine at the root of the anterior mesenteric 

 artery, being there continuous with the parietal peritoneum ; and they 

 descend, one on each side of the branches of that artery, until they 

 reach the intestine. At the concave edge of the bowel the two layers 

 separate; and after encircling the tube as visceral peritoneum, they 

 meet and become continuous at its convex or free border. Where the 

 mesentery suspends the first part of the jejunum, it is continuous with 

 the peritoneal frsenum of the duodenum ; and at its opposite extremity, 

 where it envelops the termination of the ileum, it passes on to the CEecum. 

 At the latter point it will be observed that the two layers of mesentery 

 do not become continuous around the convex border of the ileum, but 

 are prolonged beyond that, so that the terminal portion of the small 

 intestine is included in the mesentery some distance from its free edge. 



The Colic Mesentery. — This is the membrane that suspends the single 

 or floating colon. It is composed of two layers of peritoneum, which 

 leave the roof of the abdomen along a line extending from the root of 

 the anterior mesenteric artery to the inlet of the pelvis. These two 

 layers include between them the posterior mesenteric artery and its 

 branches ; and after enveloping the single colon, they become continuous 

 at its free edge. At its anterior extremity the colic mesentery is con- 

 tinuous with the great omentum and with the great mesentery, and at 

 the pelvic inlet it is continuous with the meso-rectum. 



