THORAX AND ABDOMEN OF THE HORSE 



111 



the mesenteric veins correspond in general to the branches of the 

 arteries of the same name. The cranial mesenteric vein is of large size 

 but of little length, and lies to the right of the homonymous artery. 

 The caudal mesenteric vein is of much smaller volume. The two 

 vessels are concerned — along with the splenic vein — in the formation of 

 the vena portae, of which the cranial vein forms the largest radicle. 



Numerous, flattened groups of lymph glands (lymphoglandulae 

 mesentericae) occur in the mesentery of the small intestine in the 

 neighbourhood of the cranial mesenteric artery. A few glands, small in 

 size, are to be found in association with the iliac ramus of the ileo- 

 cajcal artery. The lymph glands of the caecum and colon (lymphoglan- 

 dulae caecalis, lymphglandulse colica) are disposed in scattered linear 



Ileo-csecal opening. 



Ileum. 



Interior of body of 

 caecum. 



-colic opening. 



f dorsal sac. 



Fig. 51. — View of the interior of the ceecum showing the position of its openings. 



groups following the course of the vessels of these parts of the large 

 intestine. The glands of the small colon are to be looked for near the 

 root of the mesentery of this intestine, and also near the attachment of 

 the mesentery to the gut. 



Interior of the intestines. — The intestines should be slit open 

 and their interior examined. The internal lining is a soft, slimy mucous 

 membrane, more or less folded. In the small intestine the folds are 

 longitudinal, and may be obliterated by distension. In the large intes- 

 tine the folds or ridges are permanent, transverse to the long axis of 

 the tube, and correspond to the constrictions between the sacculations 

 observable on the exterior. Between them are saccular pouches, or 

 cellulce. 



The mucous membrane around the ileo-ca^cal opening is slightly 

 raised into a circular fold, and at the caeco-colic opening there is a 

 crescentic fold of mucous membrane. 



In the small intestine, and more particularly in the ileum, it is 



