MAMMALS. 



36 L 



more distal portions. The carpal and tarsal bones are in twcr 

 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. 176). 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 



' .... . , , FIG. 348. Fore (right) and 



man ; or upon the distal phalanges, hind (le f t ) f ee t of tapir. ,. 



as in the Cats and dogs ; Or, again, astragalus; c, cuneiforme in 



. calcaneum in hind. 



fore 



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



cuboid ; 7% femur ; /, lunare ; 



upon the nails (hoofs), as in the 

 horse and cow. 



The most Striking feature of the m, magnum; , naviculare;: 



nervous system of existing mammals *> pisiforme; A\ radius; * 



...... scaphoid ; /, trapezoid ; 7'., 



is the great size of the brain, and es- tibia . tt> unciforme; u, ulna, 

 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. 1 This great increase 

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

 a small portion of which remains epithelial in character. In 



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

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

 luted (Fig. 54). 



