OUTLINE OF THE STKUGTURE OF THE HORSE. 65 



Terminating in the anu^, (see i, in cut,) is the next and last 

 intestine, the rectum (see A, in cut). Its name signifies straight, 

 which it much more nearly is than the other bowels. It is 

 much shorter than the colon, with less than one-fourth the 

 capacity. As no portion of digestion remains to be carried 

 on here, its mucous lining is not exactly the same as in the 

 other parts of the intestines, and is entirely destitute of ca- 

 pillary absorbents. The rectum forms a capacious reservoir 

 for the excrement Until evacuated. This is retained in its 

 place by the curious circular muscle at the anus, called the 

 sphincter muscle, until the horse, by a voluntary effort, expels 

 it. By these means, IlTature prevents a constant and disagree- 

 able dropping of the foeces. 



A doubling of the peritoneum, called the mesentery, (see c, 

 in cut,) forms the means by which the intestines are chiefly 

 retained in their relative positions. It includes within its 

 folds all the intestines, extending along their entire length. 

 It is furnished with a large artery and a large vein — each 

 called the mesenteric — and is every- where filled with innum- 

 erable small vessels, that supply the bowels with blood, and 

 others which convey the extracted nutriment from the in- 

 testines to the general circulation. 



The omentum, or cawl, (not shown in cut,) is a twice doubled 

 fold of the peritoneum, thus consisting of four layers of it, 

 which are placed between the intestines and the sides of the 

 belly. By some it has been supposed to answer the purpose 

 of a soft padding, to relieve the violent concussions and pre- 

 vent the injuries which rapid motion would be likely to pro- 

 duce. It is unusually short in the horse. 



THE LIVER. 



In the horse the liver undoubtedly performs the same of- 

 fices as in the human being ; but these are involved in much 

 obscurity. It secretes the bile from the venous blood, (sup- 

 plied to it by the portal circulation,) which, if retained 

 therein, would poison the whole system; but which, when 

 mingled with the chyme, is of the highest service in the 

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