470 



Vertebrata. 



or concave below. The wall is usually covered at the base by a 

 fold of skin. The nails of Monkeys differ from most claws in 

 that the sole is very short and consists of very soft horn (this may also 

 be the case in many true claws), and that the wall is but slightly 

 curved, either longitudinally or transversely; in Man the sole has 

 practically vanished, merely an insignificant remnant of it lies below the 

 edge of the wall, and the "nail" is the wall only. The modifica- 

 tions termed hoofs, are pecuhar in that they are short with blunt 

 ends, and the thick wall is convex transversely, but not longitudinally 

 (or very slightly) ; and in that the horny sole is thick and hard, 

 and the fold of skin at the base very poorly developed. The 

 peculiarity of the hoof is correlated with its function of supporting 

 the animal when walking, whilst in other forms the sole of the 

 foot serves this purpose, and the claws are used for climbing, 

 digging, etc., and in this connection, among other points, a solid 

 attachment by means of a deep fold of skin appears of special 

 importance. 



In most Ungulata (excepting tlie Tapir and tie Rhinoceros) there is an 

 intimate connection bet-ween the hoof and the sole of the foot, which is usually 



11^ 



Fig. 381. Longitudmal 

 section of the tip of a Mam- 

 malian digit. Malpighian 

 layer dark, a and b see p. 

 471, ba ball of the foot with 

 sweat glands, g last phalanx 

 of the digit, g' next phalanx 

 (not completely drawn), h 

 cavity of the joint, p and t 

 wall, s sole, sb sesamoid bone, 

 w fold of skin at the base of 

 the claw. — Orig. 



very small here, and confined to the distal portion of the toes. In the Horse 

 (Fig. 382 JD) the hoof is, so to speak, arched round the very small sole of 

 the foot (the "frog"), so that the latter lies at the back of the hoof; relations 



Fig. 382. Tip of toes seen from below ; A Monkey, B a clawed animal, C Rhinoceros, 

 D Horse, E Elk ; diagrammatic, b sole of the foot, n edge of wall, s homy sole. — Orig. 



