FINS AND LIMBS 



3*9 



nails or hoofs. When the whole surface of the hand or foot 

 is applied to the ground, as in the human foot, the animal is 

 said to be plantigrade. Other animals, like the dog, rest only 

 the under surface of the fingers and toes on the ground, while 

 the palm of the hand and sole of the foot take no share in 



Fig. 163. — Convergence in the adaptation of limbs for flight, A, in birds ; 

 B, Pterodactyls ; C, bats. 



cm, carpo-metacarpus ; h, humerus ; mc, metacarpal ; p, phalanx ; 

 r, radius ; w, ulna. 



bearing the animal's weight. This is the digitigrade condition. 

 Others again, such as the horse and cow, which rest only on the 

 end joints of the fingers and toes, are unguligrade. [The latter 

 form part of the order Ungulata.] 



The limbs of the horse are specialised for rapid movement 

 on hard ground. Only the 3rd digit is retained, and its 



