328 End-Organs of the Trigeminus and Lateralis Nerves 
inner and an outer layer. The outer layer is, for the most part, com- 
posed of larger cells so arranged as to produce a smooth surface. As its 
cells die and fall away from the surface they are replaced from the inner 
layer. Numerous migrant mucous cells push their way from the base- 
ment membrane, lying on the dermis, outward, until they reach the 
surface where they break and discharge their contents upon the surface 
of the skin. With the exception of the mucous cells, the elements of the 
epidermis are relatively stationary. 
Besides the more numerous polyhedral cells which make up the bulk 
of the epidermis, and omitting the mucous cells already mentioned, the 
other cell types met with are the sensory cells and supporting cells of the 
sense organs, the long club-shaped cells or palisade cells, and the un- 
differentiated cells from which all of these are produced. When, instead 
of using a hematoxylin or a carmine stain, some of the coal-tar colors 
are used, it is seen that the inner layer of the epidermis is itself sharply 
divided into two layers, a broad inner layer resting directly upon the 
basement membrane, and an outer layer of varying width. In material 
that has been hardened in chromic acid, this outer layer, the middle layer 
of the epidermis, does not stain with aniline green, Lyons blue, toluidin 
blue, or saffranin, but takes picric acid easily and holds it well. As the 
superficial layer, composed of larger cells, stains in the same color as the 
inner layer, it is thus shown that the division between outer and middle 
layers is not clean cut, as it looks in hematoxylin sections, for patches 
of yellow can be seen intruding into the outer layer, and lying between 
its cells. In Golgi sections a similar division is seen. The impregnation 
is extremely capricious in its action, here as elsewhere; sometimes the 
entire inner layer will be blackened, sometimes the entire middle layer. 
When this latter is the case, the blackening will sometimes extend far up 
into the outer layer, showing better than the color stains how deep the 
doyetailing of outer and middle layers really is. 
THE TRIGEMINUS ENDINGS. 
Free endings.—First and simplest of all are what appear to be free 
endings. The fine fibers of the nerve, on entering the epidermis, divide 
into still finer fibrils, some of even diameter, some beaded. Some of these 
fibrils take a comparatively straight course through the epidermis, and 
end in the outer layer, without forming nerve plates in connection with 
