136 



COMPAKATIVK ZOOLOGY. 



and toes. Claws 

 :ire sharp conical 

 nails, being devel- 

 oped from the sides 

 as well as upper 

 surface; and hoofs 

 are blunt cylin- 

 drical claws. Hol- 

 low horns, as of the 

 Ox, may be likened 

 to claws sheathing 

 a bony core. The 

 horn of the Rhinoc- 

 eros is a solid mass 

 of epidermal fibres. 



" Whalebone 



Fig. 103.— Vertical Section of the Forefoot of the Horse 

 (middle digit) : 1, 2, 4, proximal, middle, aud distal, 

 or ungual, phalanges ; 3, sesamoid, or nut-bone ; 6, 

 6, 7, teudims; 9, elastic tissue; S, 10, iuterual and 

 external Jloor of the hoof; 11, 12, internal aud exter- 

 nal walls. 



rattles of the Rattlesnake, and tlie 

 beaks of Turtles and Birds, are like- 

 wise epidermal. 



Hairs, tlie characteristic clothing 

 of Mammals, are elongated horny 

 cones, composed of "pith" and 

 "crust." The latter is an outer 

 layer of minute overlapping scales, 

 which are directed towards the 

 point, so that rubbing a human 

 hair or fibre of wool between the 

 thumb and finger pushes the root- 

 end away. The root is bulbous, 

 and is contained in a minute de- 

 pression, or sac, formed by an in- Pm.m-secti^theRootand 

 folding of the skin. Hairs are usu- 

 ally set obliquely into the skin. 

 Porcupine's quills and Hedgehog's 

 spines make an easy transition to 



part of the Shaft of a Hnma 

 Hair; it is covered with epi- 

 dermic scales, the inner layer, 

 c, forming the outer coverinj,' ' 

 of the shaft, being imbricated ; 

 the root consists of angular 

 cells loaded with pigment. 



