THE INTESTINES. 295 



The next portion of the small intestines is the Jejunum^ so called because it 

 is generally found to be empty. It is smaller in bulk and paler in colour than 

 the duodenum. It is more loosely confined in the abdomen floating compara- 

 tively unattached in the cavity of the abdomen, and the passage of the food being 

 comparatively 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 commence. Together they form that portion of the intestinal tube 

 which floats in the umbilical region : the latter, however, 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 gradually diminishes in size as it approaches 

 the larger intestines. 



These two intestines are attached to the spine by a loose doubling of the pe- 

 ritoneum, 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 effects 

 is the cerebro- visceral nerve t. 



The large intestines are three in number : the ccecum^ the colon, and the 

 rectum. The first of them is the ccecum 

 (blind gut), c, p it has but one opening 

 into it, and consequently everything 

 that passes into it, having reached the 

 blind or closed end, must return, in order 

 to escape. It is not a continuation of the 

 iieum, but the ileum pierces the head of 

 it, as it were, at right angles, (d^ p,) and 

 projects some way into it, and has a 

 valve the valvula coli at its extremity, 

 so that what has traversed 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 accompanying side cut. 



That portion of the food which has not been taken up by the lacteals or ab- 

 sorbent vessels of the small intestines, passes through this valvular opening of 

 the ileum, and a part of it enters the colon, while the remainder flows into the 

 caecum. Then, from this being a blind pouch, and from the cellular structure 

 of this pouch, the food must be detained in it a very long time ; and in order 

 that, during this detention, all the nutriment may be extracted, the caecum and 

 its cells are largely supplied with blood-vessels and absorbents. It is principally 

 the fluid part of the food that seems to enter the csecum. A horse will drink 

 at one time a great deal more than his stomach will contain ; or even if he 

 drinks a less quantity, it remains not in the stomach or small intestines, but 

 passes on to the caecum, and there is retained, as in a reservoir, to supply the 

 wants of the system. In his state of servitude the horse does not often drink 



* Percivall's Anatomy of the Horse, p. 256. 

 j- Youatt's Lectures on the Nervous System, Veterinarian, vol. vii. p. 354. 



