228 OUTLINES OF EQUINE ANATOMY. 



the two divisions of the intestine, wHcli is most marked at 

 the sigmoid flexure, is termed the mesocolon. It presents 

 the figure of a racket bat, the broad portion of which is at 

 the sigmoid flexure. The diverging portion of the double 

 colon is also attached to the caecum by a double fold of 

 peritoneum, the mesocsecum, while the single colon floats 

 atvthe free margin of a double peritoneal fold, which, after 

 being continued for a slight distance posteriorly around the 

 anterior ^^art of the rectum (the mesorectum), is reflected la- 

 terally on to the walls of the abdomen in forming the anterior 

 boundary of the pelvis. In the large, as in the small intes- 

 tine, we find the arteries forming loops between the peritoneal 

 supporting layers from which branches run to the attached 

 margin of the intestine, where they break up in supplying 

 mainly the muscular and the mucous coats. The csBcum is 

 supplied by two branches of the anterior mesenteric artery. 

 They run towards its apex and anastomose just before reach- 

 ing it ; they send off numerous branches. The double colon 

 is supplied by two branches from the anterior mesenteric, 

 which run along the attached margins of the diverging a,nd 

 returning portions respectively, and anastomose on con- 

 verging at the sigmoid flexure. A branch from the anterior 

 mesenteric also passes to the anterior part of the single 

 colon, and posteriorly joins the first branch of the pos- 

 terior mesenteric, which breaks up in the mesorectum, 

 forming arched vessels which supply the single colon and the 

 anterior part of the rectimi, anastomosing posteriorly with 

 the hsemorrhoidal branches of the lateral sacral, by which, 

 in conjunction with branches of thp, artery of the bulb, the 

 posterior part of the rectum and the anus are supplied. 

 The veins of the large intestine converge to form the an- 

 terior and posterior mesenteric veins, which form the 

 commencement of vena portae, up against the anterior 

 mesenteric artery. The 7ierve siipijly of the large intestine 

 is conveyed by branches from the semilunar and posterior 

 meseiiteric ganglia. The latter is found in contact with 

 the artery of the same name, and sends fibres in a back- 

 ward direction, which combine to form an intricate arrange- 

 ment of nerve-fibres of the walls of the rectum in the pelvis, 

 to which the name hypogastric ])lexus is given. Numerous 

 lymphatic or lacteal glands may be seen in apposition with 

 the attached portions of the large intestine along its whole 

 length, but ^predominating in the anterior part. The vessels 



