48 The Alligator and Its Allies 
mandible. The other pair is inside of the lips of 
the cloaca. 
The Histology of the Integument. ‘To understand 
the structure of the integument of the Crocodilia 
it is well to begin with the embryo. A cross section 
of the epidermis of such an embryo will show the 
rete Malpighii as a single layer of short, cylindrical 
cells; over these are found more or less flattened, 
disk-shaped cells formed by transverse division of 
the underlying cells of the rete. On the outside lies 
the epitrichial layer which consists of a mosaic of 
polygonal cells, near the middle of each of which 
lies an oval nucleus. Between the epitrichial cells 
are small oval holes, not unlike the stomata in the 
epidermis of plant tissues. Bronn thinks these are 
not artifacts, but he does not suggest any explana- 
tion of their occurrence. 
In the epidermis of young and half-grown ani- 
mals the rete Malpighii is seen still as above noted. 
On these cylindrical cells are found flattened cells 
that gradually become very flat and lose their 
nuclei as they pass over into the horny layer. 
The stratum corneum consists of strongly flat- 
tened cells in which the nuclei can no longer be 
clearly seen, though their location can usually be 
determined by the groups of pigment granules. On 
the cells of the more superficial layers of the stratum 
corneum are seen straight, dark lines, perhaps 
ridges caused by pressure of the over- or underlying 
polygonal cells. The individual cells of the horny 
