THE HORNS. 31 
progress, and that we can see more of it than we can of the 
growth of these, that it seems to us so strange. We see horn in- 
vading skin, or skin apparently converted to horn, as we have 
never seen it before; hence it is that even the general reader feels 
a greater interest to know how this takes place, while he has felt 
no interest to inquire how his nails grow because he sees nothing 
in their growth which is exceptional, no evidence that the skin 
“is converted into nail. We shall, however, find something 
anonymous besides the rapid growth. 
First, it is necessary to inquire what is this core over which 
this horn grows and forms a shell, and what is this covering 
which envelopes it, and which appears before our eyes to be con- 
verted into horn so rapidly ? 
The core itself is a proper bone, a part of the skull itself, 
elevated at its upper part into the form observed, and is persist- 
ent through the life of the animal, as any other internal bone. 
The first covering of this bone, like that of all other bones, is a 
periosteum, traversed by arteries, which throw off great numbers 
of branches which penetrate the bone through canals, thus afford- 
ing to it nourishment, and contributing to its growth. Immedi- 
ately upon the periosteum reposes the skin without the interposi- 
tion of any muscular tissue. This consists, first, of a layer of 
subcutaneous cellular tissue, if that may be called a part of the 
skin; second, of derma, or corium; and third, epidermis. All 
these together constitute the skin which immediately overlays 
the periosteum. The naked eye is incapable of individualizing 
these separate parts composing the skin, and so it appears as if 
the whole were converted into horn, which appears to take its 
place over the periosteum; but, by the aid of the microscope, 
these different parts are plainly revealed, and we readily deter- 
mine to which the growth of the horn is due, and the exact mode 
of that growth. 
The illustrations show the epidermis and the outer section of 
the skin which overlays the periosteum. Fig. 1 under a power of 
60 diameters, and Fig. 2 magnified 296 times. These we shall the 
better understand as we proceed. 
The lightish-colored hairs previously described, which rather 
sparsely cover the skin which envelopes the core before the horn 
is formed, and on the lower part of the horn when its growth is 
completed, passing quite through it, and showing themselves on 
the outside, have their roots in the inner part of the skin tissue 
next the periosteum. 
