INTESTINAL CANAL. 29 



pale, and form a lamina not so thick as common writing paper. 

 The superficial ones are longitudinal, not very distinct, and too 

 much separated to form a perfect coat: they are most abundant 

 on the anterior semicircumference or the one most distatji from 

 the Mesentery. The others all run in a circular direction, ap- 

 proaching to the spiral, and are sufficiently numerous to form a 

 perfect coat: none of them perform a complete circuit of the in- 

 testine, but are rather segments of circles. This coat is united 

 to the peritoneal by a thin scattered cellular substance. 



The Cellular Coat of the small intestine, also called the ner- 

 vous, like that of the stomach, is only a lamina of dense cellu- 

 lar substance, which serves as a medium of connexion between 

 the muscular and the mucous coat; and also conducts to the 

 latter the blood vessels, nerves, and lacteals. When* inflated 

 and dried, it puts on a beautifu^ cotton-like appearance as in 

 fact the corresponding coat of other parts of the alimentary 

 canal does the same. 



The Mucous Coat is the most internal, and when it has been 

 cleaned by maceration, exhibits an opaque pearly colour. It is 

 remarkable for having its extent very considerably augmented 

 beyond that of the other coats; by being thrown into a great 

 number of permanent folds, or duplicatures, which lie one upon 

 another successively, like the shingles upon the roof of a house. 

 These duplicatures are the Valvulse Conniventes, and are for 

 the most part about three lines in breadth. They are either 

 placed in the direction of the circumference of the intestine, or 

 are very slightly oblique; generally they go all around, but 

 many of them are segments of circles, and by being arranged 

 successively, their ends pass one another, or are connected by 

 slight elevations. They are more numerous and broad in the 

 upper than in the lower half of the intestinum tenue, and are 

 evidently intended to retard the progress downwards of alimen- 

 tary matter, and to increase the surface for absorption and for 

 exhalation. 



The mucous membrane, on the side which it presents to the 

 cavity of the intestine, is furnished with a great number of de~ 

 licate cylindrical projections, resembling the down on the skin 

 of an unripe peach, and called Villi,* from whence the term vil- 



* This is intended merely as an expression of the common and received no- 

 tion, my own views are exhibited in the minute anatomy of this coat. SECT. in. 



4* 



