158 INTRODUCTION. 



and, in addition to this, it is decidedly serrated ; whilst hair, though 

 sometimes curled, but in a very limited degree, in comparison with 

 wool, has its edge only scaly, or rugose, and never truly serrated ; 

 and hence it is that hair, though it will entangle and harle, to a cer- 

 tain extent, will not felt into a compact mass. 



Some animals, as the Pangolins (Manis), are clad in scales (fig. 170) ; 

 some, as the Armadilloes, in plates (fig. 171). Scales, in their mode of 

 growth, and in their general characters, are closely analogous to hair; they 

 arise from the skin (cutis) by a broad base, and are of a firm and horny 

 texture ; they vary in thickness and hardness ; and when lost, by accident, 

 are replaced. It does not appear, however, that, like hair, they are 

 periodically shed and renewed ; in which respect they resemble nails. 

 The scales of snakes are covered with epidermis, which is annually cast 

 off in the form of a slough, a new epidermis being prepared beneath the 

 old ; but, in the Pangolins, the epidermis does not extend beyond the 



Scales of the I'angoliu. Pl ates of ^g Armadillo. 



base of the scales, which are imbricated, largely overlapping each other, 

 and forming a dense and efficient coat of mail. 



The Armadilloes are protected above with plates, which, instead 

 of being affixed to the skin by one edge only, as the scales of the 

 Pangolin, adhere, by the whole of their inner surface, to the cutis, and 

 are covered by the cuticle, which is thick and smooth. These plates 

 are, more or less, calcareous ; and, in one species, the Mataco (Dasypus 

 Apar, Desm.), they are completely osseous, and of great thickness. 



The digital extremities of terrestrial Mammalia, are either protected, 

 as in Man, by slender, horny laminae, termed nails, or by stronger and 

 more curved sheaths, termed claws ; or by a thick mass surrounding the 

 phalanx, termed a hoof. 



Nails, in their growth, are analogous to hairs ; they arise from a por- 

 tion fixed in the cutis, and adhering to it, termed the root. The nails of 

 Man, and the claws of other animals, appear to be formed of extremely 

 thin layers, placed one upon another ; the addition taking place on the 



