THE LIMBS 



177 



covered, for the purpose of increasing its area, with 

 slightly raised parallel longitudinal rows of papillaG, 

 indications of which may be seen in the longitudinal 

 ridges with which the surfaces of most nails are marked. 

 The nail continually grows at the base and from its inner 

 attached surface by the exudation of fresh epidermic 

 material, which pushes forward the older-formed portion. 

 This, if left to nature, eventually wears or breaks away 

 at the free edge. The portion of the derm from which 

 the nail grows is called the c matrix.' The nail of the 

 human hand is, generally speaking, flat, but its surface 

 has a considerable curve from side to side, and also, 

 though in a less degree, in its long diameter. 



In those animals which belong to the typically ungui- 

 culated or clawed groups the bone of the last phalanx 

 is long, but compressed from side to side, curved, and 

 pointed, and the two sides of the nail bend completely 

 round, so that their edges nearly meet at the middle 

 line of the back or under surface of the finger or toe. 

 In this way the nail becomes converted into a claw, 

 which forms a sheath surrounding the bone. Usually, 

 however, especially near the base, the edges do not quite 

 meet, and there is a groove between them, filled up by 

 softer epidermic material. As it is important for the due 

 fulfilment of the function of claws that they should not 

 be blunted by contact with the ground in walking, they 

 are, in their most perfect condition, raised at their ends, 



