TEGUMENTARY ORGANS 



373 



papillae (Gurlt), and a bony plate extends from the last phalanx into 

 the posterior fold of the nail. 



The transition from the claw to the //oof is readily understood if 

 we suppose the terminal portion of the former to be blunt and 

 cylindrical, instead of pointed and conical {Jig: 305.). The elephant 

 and rhinoceros do in fact afford an actual passage from the nail to the 

 hoof, inasmuch as their very flat nails are continuous at their edges 

 with the solid and horny covering of the sole (Heusinger). 



The solipede hoof has been described in the article SOLI- 

 PEDIA ; we need therefore only remark 

 here that the zua// corresponds with the 

 nail in man, and may, by maceration, be 

 separated from the sole and frog, which 

 are developed from the termination and 

 posterior surface of the phalanx. The ridge 

 or " bourrelet " at the upper margin of the 

 wall answers to the posterior nail-wall, and, 

 as in the nail, the horny upper layer of 

 the " epidermis " is continued on to the 

 hoof from it. The structure of the bed of 

 the hoof differs in its different parts. That 

 portion which corresponds with the sole and 

 frog merely presents papillae, which fit into 

 depressions of the horny ecderon ; that 

 which corresponds with the wall is produced 

 into lamellae like those of the bed of the 

 nail, so that the deep surface of the wall is 

 laminated. In addition, however, long 

 papillae extend from the " bourrelet " 

 through the superficial portion of the wall, 



so that, on section, it presents a superficial series of canals, around 

 which the horny matter is disposed in concentric layers. 



Each half of the hoof of a ruminant (Jig;. 305. B), or of the pig, 

 corresponds in general structure with the entire hoof of a solipede, 

 except that the frog is rudimentary. The horny ecderon presents 

 both tubuli and lamina. 



The excrescences on the inner surface of the leg of the horse are 

 identical with the sole of the foot in structure — consisting of a horny 

 mass penetrated by long papillse. 



The hollow horns of the Ruminantia are, to all intents and 

 purposes. Claws. The superficial cellular ecderon (epidermis) is 

 continued upon them, and, when this is removed, we come to a 



Fig. 305. — A. Section of the foot 

 in the kitten. B. In a fcEtal 

 lamb. 



