196 GENERAL ANATOMY. 



stomach and of the duodenum, broader than they are long, con- 

 stitute little blades; those of the jejunum, long and narrow, 

 are better entitled to the name of villi, and near the end oi' 

 the ilium, as well as in the colon, where they scarcely project 

 at all, they again become laminae. The villi are semi-dia- 

 phanous, their surface is smooth, and we can neither perceive 

 on their surface the openings which have been admitted with- 

 out ever being able to agree as to their number, nor in their 

 thickness, the cellular ampullae, nor vascular texture that has 

 been described; we only perceive in their gelatiniform sub- 

 stance, microscopic globules arranged in a linear series, and 

 at their base, small branches of blood-vessels and lymphatics 

 of an excessive tenuity. 



270. The anatomical texture and composition of the mu- 

 cous membrane present many varieties or differences, in differ- 

 ent parts. The foliated disposition can not be demonstrated 

 in all parts of the membrane, and, on the contrary, manifestly 

 exists in some points of it. 



In the greater part of its extent the membrane consists 

 solely in one spongy tissue, more or less soft and very varia- 

 ble as to thickness. With respect to this we must observe, 

 that in the very young foetus, and in the inferior animals of 

 the series, the external skin itself presents this character of 

 simplicity. As to the thickness, it diminishes successively 

 from the gums, palate, nasal fossa?, stomach, intestines, biliary 

 and urinary bladders, to the sinuses and divisions of the ex- 

 cretory ducts, where its tenuity becomes extreme. It is in 

 this essential part of the membrane and at its surface, that the 

 last divisions of the vessels ramify; it is from its free surface 

 that arise the villosities. 



171. But slight traces of a distinct layer of the mucous 

 body is to be found in it, unless we regard as such, the layer 

 of coagulable fluid, that separates the papilla? of the tongue 

 from the epidermis, or consider the gelatiniform surface of the 

 villosities as belonging to it, or admit as proofs of its exist- 

 ence the ephelides or variously coloured spots that are some- 

 times found in the teguments of the glans penis and of the 

 vulva, as well as the accidental imperfect horny productions, 



