MAMMALS. 



36L 



more distal portions. The carpal and tarsal bones are in two- 

 or three rows, those of the distal row being opposite or alter- 

 nate with the others. In the tarsus the os calcis and astragalus 

 are the most prominent, the former being the fibulare, the latter 

 fused tibiale and intermedium (p. 1 76). The digits are typically 

 five in number, but Pedetes presents structures usually inter- 

 preted as a sixth toe. The tendency is constantly towards re- 

 duction in the number of digits, disappearance being preceded 

 by a reduction in length, in which 

 case the metacarpals are shortened 

 and are occasionally reduced to splint 

 bones. In certain groups there fre- 

 quently occurs a fusion of the two 

 middle metacarpals. The phalanges 

 in the digits never exceed three, ex- 

 cept in the whales. Mammals are 

 spoken of as plantigrade, digitigrade, 

 or unguligrade, accordingly as they 

 walk upon the whole metacarpal or 

 metatarsal region, as in the bear and 

 man ; or upon the distal phalanges, 

 as in the cats and dogs ; or, again, 

 upon the nails (hoofs), as in the 

 horse and cow. 



The most striking feature of the 

 nervous system of existing mammals 

 is the great size of the brain, and es- 

 pecially of the cerebrum and cere- 

 bellum, the former overarching twixt and mid brains and reach- 

 ing the latter. In the lower mammals the cerebral surface is 

 smooth, but in the higher it is marked by gyri and convolu- 

 tions, the effect of which is to increase the amount of sur- 

 face and consequently of gray matter.' This great increase 

 of the cerebrum is largely an increase of the pallium, only 

 a small portion of which remains epithelial in character. In 



Fig. 348. Fore (right) anJ- 

 hind (left) feet of tapir. a,. 

 astragalus; c, cuneiforme in-. 

 fore foot, calcaneum in hind, 

 foot; c" , c'" , cuneiforme; cb,, 

 cuboid ; F, femur ; /, lunare ; 

 77;, magnum; 7?, naviculare;; 

 p, pisiforme ; 7?, radius ; i,, 

 scaphoid ; t, trapezoid ; 'J\. 

 tibia ; it, unciforme ; U, ulna. 



1 By some authors the mammals are sub-divided into two groups, — Ineducabilia, with, 

 smooth cerebra (Fig. 349), and Educabllia, in which the surface of the cerebrum is convo- 

 luted (Fig. 54). 



