THORAX AND ABDOMEN OF THE HORSE 107 



stomach, where it is continuous with the ventral sheet of the greater 

 omentum, as has ah'eady been discovered. 



On the left side of the abdomen, the peritoneum leaves the surface 

 of the diaphragm and the left kidney as the suspensory ligament of the 

 spleen, whence it can be traced into the greater omentum. On the 

 right side the line of reflection is somewhat more complicated. From 

 the diaphragm and the liver the peritoneum passes to the duodenum and 

 the dorsal surface of the pancreas. From the edge of the pancreas and 

 the right kidney the reflection is to the base of the caecum and the 

 terminal part of the large colon, from which point two lines diverge. 

 To the right the peritoneum passes to the terminal part of the 

 duodenum ; to the left it is applied for a time to the left kidney, from 

 which it is continued as the ventral layer of the suspensory ligament 

 of the spleen. 



Behind the termination of the large colon is the root of the 

 mesentery, that fan-like sheet of peritoneum connected with the small 

 intestine, and by way of which vessels and nerves gain access to the gut. 

 Behind the root of the mesentery is a transverse fold stretching from 

 the commencement of the small colon to the duodenum. 



The colic mesentery, associated with the small colon, is reflected 

 from the dorsal wall of the abdomen along a line that extends from the 

 ventral surface of the left kidney backwards into the cavity of the pelvis. 



A detailed examination of the arrangement of the peritoneum in 

 association with the liver had better be postponed until that organ is 

 considered. And the disposition of the peritoneum in the pelvis should 

 be examined along with the viscera with which it is connected. 



Dissection. — Owing to the large size of the intestinal mass in the 

 horse, it is very difficult to dissect the blood vessels in the orthodox 

 fashion. Unless the dissection subject is quite small, it is permissible 

 to remove most of the intestines and examine the vessels after they 

 have been severed. 



The removal of the intestines should be performed with care, or 

 other organs, notably the pancreas, will suffer injury. Proceed as 

 follows. Pull the cajcum and great colon as far towards the left as 

 possible. Then liberate the terminal part of the colon and the dorsal 

 sac of the caecum from their attachment to the dorsal wall of the 

 abdomen. This should be done as far as possible with the fingers, the 

 knife, however, being needed to sever the cranial mesenteric vessels. 

 Next cut along the mesenteries of the small intestine and the small 

 colon, keeping within a few centimetres of the border of the intestine. 



Apply two ligatures, a short distance apart, round the small colon 

 about the point where it enters the pelvis, and sever the gut between 

 them. Do the same close to the junction of the duodenum and jejunum. 



Now proceed to examine the branches of the cranial and caudal 

 mesenteric arteries and veins. The proper cleaning of the arteries is 

 rendered difficult by the presence of a network of sympathetic nerves 

 around them. These nerves should be preserved. 



