THE ORAL CAVITY. 



ing little elasticity or firmness ; it may be detached in 

 considerable flakes by macerating and scraping the mucous 

 membrane, and also by the use of acetic acid. Its elements 

 . are, throughout, nucleated cells, whose arrangement and struc- 

 ture strongly recall those of the epidermis ; they are not, as 

 in the latter case, distinguishable into two sharply defined 

 laminae, but constitute one connected layer, more resembling 

 the mucous layer, but representing the horny layer also. The 

 cells are thus disposed, from within outwards : immediately 

 upon the free surface of the mucous membrane, and upon the 

 papilla, rest many layers of small vesicles of 0*004 — O , 005 ,// 

 (fig. 167), the deepest of which are, almost without excep- 

 tion, elongated and larger (0'006 — 0009'"), and disposed per- 

 pendicularly. To these succeed many layers of roundish, 

 angular, flattened cells, which gradually increase in size, be- 

 come flatter from within outwards, and assume a more and 

 more distinctly polygonal form (fig. 168, b). 



Fig. 168. 



On the outer surface, finally, we meet, gradually proceeding 

 from the deeper cells, with a few layers of the so-called epithe- 

 lial plates (fig. 168, a), that is, large (0'02 — 0-036'") bodies 

 with rounded corners, in which the flattening has gone so far 

 that they no longer deserve the title of vesicles. 



All these cells possess a delicate membrane, easily demon- 

 strable by alkalies and acetic acid; clear contents, present in 

 greater or smaller quantity, according to the amount of flatten- 

 ing, with frequently a few fatty granules, and invariably a 



Fig. 168. Epithelial cells of the oral cavity of Man : a, large ; b, middle-sized ; 

 e, the same with two nuclei ; x 350. 



