66 THE DARWINIAN THEORY 



gap between reptiles and birds, in this sense that 

 they enable us to picture to ourselves forms from 

 which both birds and reptiles as we know them 

 could have sprung. The Pterodactyl shows how 

 flight is possible to a reptile, and is possibly 

 related to birds, although this point is doubtful. 



(Fig- 7-) 



The most famous instance of geological evidence 



Fig. 7. 



4 rx^mB 



Flying Reftile (Diagrammatic Figure). 



is found in the Horse, and, although familiar, is so 

 important as to bear repetition. The typical number 

 of toes and fingers is five, as in ourselves. In 

 quadrupeds generally the number is reduced, but the 

 horse, zebra, and ass stand alone in having only one 

 digit on each foot, corresponding to the middle 

 finger and toe. If we compare the foot of the horse 

 with that of man, we find the "hock" of the horse 

 corresponds with man's heel; the "cannon-bone" 

 is the metacarpal ; the " pasterns " form the first two 



