240 OUTLINES OF EVOLUTIONARY BIOLOGY 



walk and rest on the extreme tips of one or two toes only. The 

 assumption of this " unguligrade " condition is accompanied by 

 elongation of the limb and especially of the remaining 

 metapodial bones (metacarpals and metatarsals), so that the wrist 

 and ankle in the horse, for example, are uplifted high above the 

 ground and form the so-called knee and hock respectively (Fig. 95). 



FIG. 96. Skeleton of (A) the right fore Foot and (B) the right hind Foot 

 of a Tapir, X . (From photographs.) 



c. carpals ; m.c. metacarpals ; m.t. metatarsals ; ph. phalanges ; t, tarsals ; II V, digits. 



It is also accompanied by a reduction of the ulna in the fore limb 

 and of the fibula in the hind limb to mere vestiges. Thus the 

 entire limb becomes long and slender and adapted for rapid 

 locomotion by running on hard open ground. 



The disappearance of digits from the manus and pes in the 



Mammalia follows a very simple law. The first to disappear is 



^ always the preaxial digit (No. I), which i& the shortest of the 



series (having only two phalanges while the remainder have 



