128 EQUINE ANATOMY. 



Blood Supply, — Caecal vessels. 

 Nerves. — Sympathetic. 



Large Colon. 



About twelve feet long ; it begins at the caecum, passes forward, 

 then bends backward and to the left, forming the stipra-siernal 

 curvature, lying above the sternum, then backward, turns again, 

 ionnmg pelvic flexu?'e ; runs forward to the diaphragm, forming a 

 flexure of the same name, then passes back with first portion, ter- 

 minating in the small colon, after diminishing in calibre. 



Coats. 



Serous does not completely cover it. 



Muscular and 7?iucous same as ca;cum. 



Blood Supply. — Colic vessels. 



Nerves. — Sympathetic. 



Small Colon. 



About ten feet long ending in the rectum. Has two longitudi- 

 nal bands of fibres, and is lodged in the left flank. 

 Coats. 



Same as preceding. 



hiterior shows folds like large colon which mould faeces. 

 Vessels, small and great mesenteric. 



Rectum. 



About two feet long, from the pelvic inlet to its outlet, ending 

 in the anus. 



It is very dilatable ; has no ridges, and is in relation to the 

 sacrum above and the genito-urinary organs below. The suspen- 

 sory ligaments of the penis form a ring around its posterior portion. 



Coats. 



Serous is incomplete behind. 



The other coats are like those of colon. 



Anus. 



The posterior opening of the alimentary canal ; is situated under 

 the base of the tail. It receives an aggregation of the circular 

 fibres, which form the internal sphiticter. 



External Sphincter arises from the base of the tail, includes 

 anus, and ends in perineal muscles. 



Action, by constant tension, keeping anus closed. 



