136 



COMPARATIVE ZOOLOGY. 



12 



Pro. 103. Vertical Section of the Forefoot of the Horse 

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

 or ungual, phalanges ; 3, sesamoid, or nut-bone ; 5, 

 6, 7, tendons ; 9, elastic tissue ; 8, 10, internal and 

 external floor of the hoof; 11, 12, internal and exter- 

 nal walls. 



and toes. Claws 

 are 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," the 

 rattles of the Rattlesnake, and the 

 beaks of Turtles and Birds, are like- 

 wise epidermal. 



Hairs, the 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- Fi & .io4.-secti^ftheRootand 

 folding of the skin. Hairs are usn- ^'^ * ^' 



ally Set obliquely into the Skin. dermic scales, the inner layer, 



_. , , . -, -r-r -, , c forming the outer covering 



Porcupines quills and Hedgehogs of the shaft, being imbricated; 



, i . . the root consists of angular 



spines make an easy transition to ceils loaded with pigment. 



