294 THE INTESTINES. 



/ The beginning of the colon. 



g The continuation and expansion of the colon, divided, like the caecum, into cells. 



A The termination of the colon in the rectum. 



i The termination of the rectum at the anus. 



The intestines of a full-grown horse am not less than ninety feet in length. 

 The length of the bowels in different animals depends on the nature of the 

 food. The nutritive matter is with much more difficulty extracted from vege- 

 table than animal substances ; therefore the alimentary canal is large, long, and 

 complicated in those which, like the horse, are principally or entirely fed on 

 torn or herbs. They are divided into the small and large intestines ; the former 

 of which occupy about sixty-six feet, and the latter twenty-four. 



The intestines, like the stomach, are composed of three coats. 



The outer one consists of the peritoneum — that membrane which has been 

 already described as investing the contents of the abdomen. By means of this 

 coat, the intestines are confined in their proper situations ; and, this membrane 

 being smooth and moist, all friction and concussion are prevented. Did the 

 bowels float loosely in the abdomen, they would be subject to constant entangle- 

 ment and injury amid the rapid and violent motions of the horse. 



The middle coat, like that of the stomach, is muscular, and composed of two 

 layers of fibres, one running longitudinally and the other circularly ; and by 

 means of these muscles, which are continually contracting and relaxing in a 

 direction from the upper part of the intestines to the lower, the food is pro- 

 pelled along the bowels. 



The inner coat is the mucous or villous one. It abounds with innumerable small 

 glands, which secrete a mucous fluid to lubricate the passage and defend it from 

 irritating or acrimonious substances ; and it is said to be villous from its soft 

 velvet-like feeling. This coat is crowded with innumerable minute orifices 

 that are the commencement of vessels by which the nutritive part of the food 

 is taken up ; and these vessels, uniting and passing over the mesentery, carry 

 this nutritive matter to a proper receptacle for it, whence it is conveyed into 

 the circulation, and distributed to every part. 



The intestines are chiefly retained in their relative positions by the mesentery, 

 r, (middle of the intestines), which is a doubling of the peritoneum, including 

 «ach intestine in its folds, and also inclosing in its duplicatures the arteries, 

 the veins, the nerves, and the vessels which convey the nutriment from the 

 intestines to the circulation. 



The first of the small intestines, and commencing fromtheright extremity of the 

 stomach, is the duodenum, a, a very improper name for it in the horse, for in that 

 animal it isnearly two feet in length. It is the largest and shortest of all the small 

 intestines. It receives the food partially converted into chyme by the digestive power 

 of the stomach % and in which it undergoes another and very important change ; 

 a portion of it being converted into chyle. It is here mixed with the bile and 

 the secretion from the pancreas, which enter this intestine about five inches 

 from its commencement. The bile seems to be the principal agent in this 

 change, for no sooner does it mingle with the chyme than that fluid begins to be 

 separated into two distinct ingredients — a white thick liquid termed chyle and 

 containing the nutritive part of the food, and a yellow pulpy substance, the 

 innutritive portion, which, when the chyle is all pressed from it, is evacuated 

 through the rectum. 



* The' conversion of food into chyme is part of the duodenum a kind of second sto- 



very imperfectly performed in the stomach of mach, to mix up and dissolve the food. That 



the horse, on account of the smallness of that apparatus is evident enough until we arrive at 



viscus, and the portion of it which is occupied the pancreatic and biliary orifices, 

 by cuticle : therefore, he needs in the upper 



