45 
In the cuticle, it is obvious that the horny portion is 
formed of cells derived from the deeper part and progressively 
finding their way to the surface where they are cast off ; but 
the elongated form of the cells resting on the dermis, and the 
size of these as compared with those above them, shows that 
in this part there is another mode of growth not yet suffi- 
ciently investigated. The epithelium of the cornea, whilst 
it presents the same general arrangement of parts as the 
cuticle, is a much more delicate structure; and on account 
of the individual cells being more readily separated, it is 
much more easily examined : it may be studied without 
much difficulty with the aid of carmine-staining and bi- 
chromate of potash. In the human subject the deepest layer 
of the corneal epithelium consists of cells not more elongated, 
in comparison with those superficial to them, than the deepest 
cells of the cuticle ; but in the ox, the sheep, and the horse, - 
and probably other animals, it presents the appearance of a 
stratum of columnar epithelium, the cells of which are as 
elongated in form as those of any columnar epithelium in the 
body. In the ox the cells are of large size. The elongated 
cells now mentioned, flat at one extremity, and pointed or 
caudate at the other, differ from those of columnar epithe- 
lium, not only in forming the deepest instead of the most 
superficial layer, but in having the flat extremity resting on 
the subjacent parts. The whole thickness of the epithelium, 
when swollen by the action of the bichromate, can be easily 
detached from the surface of the cornea, "which is left quite 
clear of any structure from which the epithelium could be 
derived ; for the only nuclei which it exhibits are the long- 
shaped nuclei in its interior, which are totally different in 
appearance from the nuclei of the epithelium. When the 
detached epithelium is examined in vertical sections, the 
elongated elements forming its deepest, layer are seen to 
lie closely together with their flattened extremities in a line, 
and each cell exhibiting only one nucleus, which is always 
at a considerable distance from the corneal extremity. Thus 
it is very obvious that the epithelium is not derived from the 
subjacent cornea, but that the cornea and epithelium are 
•wholly independent structures adhering together. 
Immediately superficial to the columnar stratum is a layer 
of cells of irregular shape, about twice as broad as the 
columnar, but by no means so elongated. They are rounded 
and even in outline at the superfical extremity, but are 
jagged at the other, sending in processes or digitations which 
may be three or four in number, and which appear to fit in 
between the tapering points of the columnar cells. The cells 
