648 TEGUMENTARY ORGANS. 



face of the nails, and become compressed, flattened, and 

 compactly agglutinated together on the upper surface and the 

 protruded part, where the stratified arrangement is most 

 apparent, and where the nuclei and contents of the cells have 

 mostly disappeared. Layers of cells are secreted and added 

 along the whole inferior attached, concave, lamellated surface, 

 to compensate for the flattening and thinning of the upper 

 convex strata of cells, first added from behind and from be- 

 neath, and thus to preserve the equal thickness and strength 

 of the nail at its free, exposed part. The nails b.eing thus 

 only the thickened epidermis of the parts which support 

 them, they adhere in the same manner as epidermis, to the 

 subjacent sensitive and vascular laminated surface of the 

 cutis, by means of the soft, homogeneous, adhesive cytoblas- 

 tema which envelopes, nourishes, and unites together the 

 growing component cells. 



The anterior vertical portion of the hoofs of ruminantia 

 and solidungula consists merely of a large curved nail, and 

 the inferior horizontal portion, which is partially attached to 

 the former along its anterior thick margin, is only the usual 

 thickened epidermis, covering the lower surface of the toes. 

 The vertical curved portion of the hoof, analogous to the 

 human nail, embraces a large part of the anterior and lateral 

 surface of the toe, is more deficient behind, and extends 

 downwards beyond the plain of the inferior basilar plate, so 

 as to defend the entire lower margin of the hoof, which is 

 most subjected to pressure and attrition. In the feet of 

 solidungula the entire anterior portion of the hoof is formed 

 as a single investing independent nail, and extends beyond 

 the inferior thickened epidermic plantar portion. The sharp, 

 dense, compressed, curved claws of feline carnivora, are nails 

 which almost invest the terminal phalanges of the toes, and 

 have their base and its containing follicle supported by an 

 osseous sheath; they are kept sharp at the point by the 

 periodical shedding of their terminal laminee. Even the per- 

 manent vaginiform horns of antilopes and other ruminantia, 

 are formed and developed like conical nails around the 

 tuberosities of the frontal bone, receiving their means of 

 increment in their interior cavity and around their follicular 

 base, like the tusk of an elephant, or the bill of a bird, a 

 tortoise, or a cephalopod, or the conical shell of a gasteropod. 

 And the solid nasal or frontal horn of the rhinoceros is 



