DIGESTIVE SYSTEM. 255 



the size and seats of which vary somewhat in the different in- 

 testines : these secrete a glairy, mucous fluid, which they pour 

 forth upon the surface of the membrane, in order to sheath and 

 defend it from the acrimony or mechanical irritation of the ali- 

 ment (as well as from any supplementary mechanical or chemical 

 irritant), and also to facilitate its passage through them. In the 

 small intestines of the human subject, this coat is collected into 

 numerous transverse folds, called valvule cotinivetites, from their 

 being supposed to have the effect of so many imperfect valves : 

 but in those of the horse no such structure exists, it not being 

 requisite (for reasons I shall hereafter give) either to retard the 

 passage of the aliment here, or to multiply the lacteal apparatus. 

 Having described the appearance and structure of the intestines 

 in general. I shall proceed to point out the peculiarities of them, 

 beginning with the 



Small Intestines. 



The small intestines are much smaller and also more uniform 

 in their caliber than the large, and exceed them greatly in length. 

 They are constituted of three parts or subdivisions, named the 

 duodenum, jejunum, and ileum. 



THE DUODENUM is more capacious than either of the 

 others, especially at its beginning, but in length is much in- 

 ferior to them : its name* is inapplicable in the horse, for it is 

 nearly twice twelve inches long. I have already given its situa- 

 tion, course, and connexions — I have no need therefore to enter 

 again into their detail here ; all I wish to repeat is, that it be- 

 gins at the pylorus of the stomach, and, having crossed the spine, 

 terminates in the jejunum. It not only differs from the others 

 in being larger and shorter, and in being straighter, but in being- 

 redder — more vascular than either of them. It is however at 

 once distinguished from all the other guts, both large and small, 

 by receiving the ducts of two important glands, situated near it, 

 viz. the liver and pancreas : these tubes terminate by one com- 

 mon orifice upon its internal coat, about the distance of six 

 inches from the pylorus. Unlike the jejunum or ileum, the 

 duodenum receives only a partial covering from the peritoneum : 

 the membrane is reflected only upon its inferior and lateral 

 parts ; the superior surface being attached to the liver, kidney, 

 and spine, by cellular tissue only. Its motions are exceeding 

 hmited. 



* Duodenum. From duodenus, consisting of tweh'e ; so called, because 

 it was not supposed to exceed the breadth of twelve fingers : but as the 

 ancients dissected only animals, this does not hold good in the human sub- 

 ject. — Hooper's Lexicon Medicum. 



