THE HORSE. 



109 



the articular extremity of the ischium. Ex- 

 tending from before backward, and rather 

 upward, they blend with the external 

 sphincter. Their action is obviously that 

 of retracting the anal opening. 



VESSELS, NERVES, AND LYMPHATICS OF THE 

 INTESTINE. 



The intestinal canal, as a whole, receives 

 arterial blood from the anterior and poste- 

 rior mesenteric arteries, hepatic branch of 

 the coeliac axis, with branches from the in- 

 ternal pudic. The arteries of the small in- 

 testine are derived from the anterior mesen- 

 teric, whose divisions, varying from twenty- 

 four to twenty-eight, proceed to the small 

 intestine, with the exception of four, which 

 minister to the nutrition and functions of 

 the large intestine. The branches extend- 

 ing from the main trunk, at acute angles, 

 proceed between the layers of the mesen- 

 tery, to within one and a half or two inches 

 from the gut, where they anastomose, form- 

 ing vascular arches, from which the second- 

 ary branches arise, and, proceeding on to the 

 intestine, ramify on the several coats, espe- 

 cially the mucus one. The anterior division 

 of the anterior mesenteric artery, proceeding 

 to the duodenum, anastomoses with the duo- 

 denal branch of the hepatic artery. The 

 last iliac division inosculates with the csBcal 

 and colic branches of the same trunk. 



The cBBCum and colon receive arterial 

 blood solely from the branches derived from 

 the anterior mesenteric, with a slight contri- 

 bution from the posterior mesenteric arteries. 

 The branches of the former originate oppo- 

 site the flexure made by the caecum and 

 colon. The cscal divisions, two in num- 

 ber, proceed downward and forward till 

 they reach the gut. The posterior one 

 passes round the posterior part of the bor- 

 der of the caecum, to get on the under sur- 

 face of the latter, extending to the apex, in 

 somewhat a straight course, and ramifying 

 collaterally ; at its termination it forms a 

 vascular network, by anastomosis with the 

 superior caecal artery. The latter one, reach- 

 ing the gut, extends directly forward towards 

 the apex, and comports itself like the former. 



Thus we see the flexure, formed by the 

 caecum and colon, is supplied by collateral 

 branches, from the superior and inferior 

 cascal mesenteric divisions, both these anas- 

 tomosing on the corresponding surfaces with 

 the colic arterial trunks. 



The two branches going to the colon ex- 

 tend, about parallel to each other, down- 

 wards and forwards and to the left, the one 

 gaining the cascal end of the colon, whilst 

 the other proceeds on to the hepatic flexure. 

 Then these may be traced, the one back- 

 ward and the other forward, relatively to 

 the course of the gut, along its superior 

 border, so as to reach the sigmoid flexure, 

 where they mutually inosculate. From the 

 mesenteric division going to the transverse 

 colon, is a branch proceeding on to the 

 single portion, which anastomoses poste- 

 riorly with the posterior mesenteric. This 

 vessel divides first into two branches, i. e. 

 an interior colic and a posterior rectal one. 

 The anterior colic branch is directed for- 

 ward and downward between the layers 

 of the meso-colon, and divides into four or 

 five branches, which bifurcate and form 

 arches, like the arteries of the small intes- 

 tine, for the supply of the contiguous gut. 

 The arteries of the rectum are sometimes 

 spoken of as haemorrhoidals, and these are 

 distinguished as anterior, middle, and pos- 

 terior. The anterior hasmorrhoidals are 

 formed by the hindermost branch of the 

 posterior mesenteric artery, which, passing 

 into the folds of the meso-rectum, supplies 

 consecutive branches to the gut, till, poste- 

 riorly to the peritoneum, where the arteries 

 pierce the muscular coat, and, forming a 

 network of vessels, anastomose with the 

 middle haemorrhoidals, which are the ramifi- 

 cations of the internal pudic* These inos- 

 culate with the posterior haemorrhoidals 

 derived from the same source. The anus 

 is then supplied with blood from the last 

 named branches, as well as from perineal 

 twigs of the external pudic. 



The veins of the intestine accompany the 



* This artery sometimes, erroneously, goes by the name 

 of its terminating branch — the artery of the bulb. 



