vi i. J THE EXTERNAL SKELETON. 245 



The human nails differ in shape from those of almost every 

 other animal, in that they so little tend to surround or enclose 

 the ends of either the fingers or toes. 



The nail at its maximum of development quite surrounds 

 and encloses the last joint of the digit which bears it, and is 

 then called a hoof, as we may see in the Horse or Ox. 



It may be produced into a sharp point, when it is called a 

 claw, as in the familiar case of the Cat, and in Birds. 



The nails may, on the other hand, be much reduced in 

 size, and not nearly extend to the end of the digits which 

 support them, as in the Sea Bear. They may be altogether 

 wanting in man's own class, as in the Porpoise, or obtain a 

 prodigious relative size, so that the body can be suspended 

 by them, in progression, as in the Sloth. The little Bats of 



F,r -> Curvru FlG. 212. HEAD OF MALE OF 



0. 2II.-SLOTH. , 



our own country hang, indeed, by hook-like claws when at 

 rest ; either by the claws of the toes or the two thumb-claws. 



The nail of one digit may differ in form from all the others, 

 as in that of the second toe of Lemurs and of the Hyrax. 



The nail makes its appearance in its greatest simplicity in 

 certain Toads and one of the Efts, where it is merely a slight 

 thickening of the epidermis at the ends of the digits. 



12. ECTERONIC APPENDAGES not found in man make their 

 appearance in other animals. Thus, in the Rhinoceros we 

 meet with a horn (or even two one in front of the other), 

 entirely destitute of a bony core, and growing like a great 

 blunt nail from the dorsum of the muzzle, long dermal papillae 

 extending into it and answering to the dermal ridges beneath 

 the human nail. 



No less than three long horns are developed in Owen's 

 Chameleon one from the nose, and a symmetrical pair from 

 the front of the head. 



Other horns which do possess bony cores are developed 

 from the head in pairs in the so-called hollow-horned Rumi- 

 nants, i.e. the Oxen, Antelopes, Goats, and Sheep ; and only 

 in one anomalous form, the Prongbock (Antilocapra\ are 



