THE INTESTINES. 



229 



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

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

 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 hrst of the small intestines, and commencing from the right extremity of the 

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

 mal it is nearly 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 chi/le. 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 next portion of the small intestines is the Jejunum, so called because it is 

 generally found to be empt}'. It is smaller in bulk and paler in colour than the 

 duodenum. It is more loosely confined in the abdomen — floating comparatively 

 unattached in the cavity of the abdomen, and the passage of the food being com- 

 paratively rapid through it. 



There is no separation or distinction between it and the next intestine — the Ileum. 

 There is no point at which the jejunum can be said to terminate and the ileum com- 

 mence. Together they form that portion of the intestinal tube which floats in the 

 umbilical region : the latter, hov/ever, is said to occupy three-fifths, and the former 

 two-fifths, of this portion of the intestines, and the five would contain about eleven 

 gallons of fluid. The ileum is evidently less vascular than the jejunum, and gradu- 

 ally diminishes in size as it approaches the larger intestines. 



These two intestines are attached to the spine by a loose doubling of the peritoneum, 

 and float freely in the abdominal cavity, their movements and their relative positions 

 being regulated only by the size or fulness of the stomach, and the stage of the 

 digestive process.]" 



The small intestines derive their blood from the anterior mesenteric artery, which 



divides into innumerable minute branches that ramify between their muscular and 



villous coats. Their veins, which are destitute of valves, return the blood into the vena 



cava. The prime agent in producing all these eflfects is the cerebro-visceral nerve. :|: 



The large intestines are three in number: — the csecum, the colon, and the rectum. 



The first of them is the csecum (blind gut), e, 

 — it has but one opening into it, and con- 

 sequently everything tiiat passes into it, having 

 reached the blind or closed end, must return, 

 in order to escape. It is not a continuation of 

 the ileum, but the ileum pierces the head of it, 

 as it were, at right angles, ( rf, ) and projects 

 some way into it, and has a valve — the valvula 

 coli — at its extremity, so that what has tra- 

 versed the ileum, and entered the head of the 

 colon, cannot return into the ileum. Along 

 the outside of the caecum run three strong 

 bands, each of them shorter than that intestine, 

 and thus puckering it up, and forming it into 

 three sets of cells, as shown in the accom- 

 panying side cut. 



That portion of the food which has not been 



* The conversion of food into chyme is very imperfectly performed in the stomach of the 

 horse, on account of the smallness of that viscus, and the portion of it which is occupied by 

 cuticle : therefore, he needs in the upper part of the duodenum a kind of second stomach, to 

 mix up and dissolve the food. That apparatus is evident enough until we arrive at tba pan- 

 creatic and biliary orifices. 



tPercivall's Anatomy of the Horse, p. 256. 



t Youatt's Lectures on the Nervous System, Veterinarian, vol. vii. p. 354. 

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