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 liow 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 individuahzing 

 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. 



