268 



DIGESTIVE ORGANS. 



[sect. 129. 



membrane, agreeing more with the mucous layer of the epidermis, 

 although, also, representing the horny layer. The relation of the 

 cells from within outwards is the following : — Immediately upon 

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

 are seated several layers of small vesicles, o , oo4'" to 0'005"' in 

 diameter (fig. 109), of which the deepest are almost invariably 

 elongated and larger (o , oo6'" to 0*009'"), anc ^ disposed perpendi- 

 cularly to the mucous membrane. Then follow many layers of 

 rounded, angular, flattened cells, which gradually increase in size 

 and flatness from within outwards, and continually assume more 

 and more of a polygonal form (fig. no, b). Most externally, we 



Fig. 110. 



Epithelial cells in the oral cavity of man. a. Large; b. middle sized ; c. the same with 

 two nuclei. Magnified 350 times. 



find some more layers of epithelial plates (fig. no, a), as they are 

 termed, which are gradually formed from the deeper cells ; they 

 are very large (0*02'" to o - o36'"), rounded, angular scales, in which 

 the process of flattening has so far advanced, that they can no 

 longer be properly called vesicles. 



All these cells have a thick cell-membrane, which is readily 

 demonstrable by alkalies and acetic acid, and contain, according to 

 the degree of flattening, a larger or smaller amount of clear 

 contents, frequently with some fat-granules, and invariably a cell- 

 nucleus. In the smallest cells, the nuclei measure 0*002'" to 

 0003'", are elongated or round, and mostly without a distinct 

 nucleolus • in the polygonal cells, there are invariably found one or 

 two very beautiful, distinctly vesicular, mostly spherical nuclei, of 

 0*004"' to 0006'" in size, with clear contents and one or two nu- 

 cleoli. In the plates, finally, the nuclei enter upon a retrogressive 

 process, have become smaller again, o'ooV to 0*005'" m length, 

 0-002"' to 0*0015'" in breadth, are mostly flattened and more 



