254 DIGESTIVE SYSTEM. 



Division. — These viscera are divided into the small and large 

 intestines : the latter, as their name impUes, exceed in volume 

 the former. Each of these divisions is subdivided into three 

 parts ; and these have each of them a particular name. I shall 

 take into consideration the general structure of these tubes, in 

 which they all agree, before I proceed to a detail of their 

 differences. 



General Structure. — An intestine is composed of three coats : 

 the first or external is called the peritoneal ; the second or mid- 

 dle, the muscular ; and the third or internal, the villous or mucous 

 coat. 



The peritoneal coat is simply a covering continued from the 

 peritoneum itself, which includes the mesenteric vessels and 

 nerves in its way to the intestines, and connects them to the 

 spine, to one another, and to other viscera. It intimately ad- 

 heres by fine cellular membrane to the muscular coat under- 

 neath. It serves to strengthen the tubes ; to furnish a lubri- 

 cating serous perspiration ; and either to restrain their motions 

 within certain limits, or to confine them altogether to their 

 places. 



The muscular coat, like that of the stomach, is composed of 

 two orders of fibres: — a longitudinal, running immediately un- 

 derneath the peritoneum, and consisting of a few pale scattered 

 fasciculi: and a circular, of which the fibres are placed more 

 inwardly, are stronger, more numerous, and more distinct. By 

 a combination of both their actions, the intestine may be con- 

 tracted in every direction ; for while the former will have a ten- 

 dency to shorten it, the latter order of fibres will operate forcibly 

 in diminishing the caliber of its canal: it is the circular fibres, 

 however, that are principally called on for action ; by their opera- 

 tion the aliment is propelled gradually through them. 



The villous or mucous coat of the intestines, though in ge- 

 neral appearance it resembles the one of the stomach, differs 

 from it in many essential particulars. It is also of infinitely 

 greater extent, presenting a surface for absorption and secretion, 

 exceeding even that of the common integuments, lis villi {more 

 especially in the small intestines), instead of consisting principally 

 of minute bloodvessels, are crowded with lacteals, which are 

 supposed to take their origin from them by open mouths. And 

 besides the villi, its interior is studded with numerous glandules, 



intestinal canals, I have taken as the data of my calculation. Whatever 

 objections they may be liable to, we may at least draw this conclusion from 

 them, — that the intestines of a horse exceed in proportionate length those 

 of a man. 



