A CONCLUSIVE INSTANCE 50 



appear to wander). The hen, for instance, does 

 not have five fingers in her wings, vertebrate though 

 she be. In point of fact, she has three and a half 

 fingers in each wing, as a simple dissection demon- 

 strates. What, then, becomes of our theory that 

 the typical vertebrate hand is pentadigitate, and our 

 inference that this is presumptive proof of the evolu- 

 tion of all vertebrates from a common stock ? We 

 answer by asking you now to dissect the embryonic 

 form of the hen. When we examine the embryo 

 chick, it is found to have a five-fingered hand. Later, 

 one and a half fingers, which are found to be super- 

 fluous for the due efficiency of the wing in its new 

 role as an organ of flight, undergo atrophy, and dis- 

 appear. You are tempted to suggest that this 

 formation of more fingers than are to persist is 

 somewhat pointless and lacking in economy. That 

 may be, but it at least serves this purpose : that it 

 is an instance of a fact which, on the theory of 

 organic evolution alone, is capable of a rational 

 interpretation. 



Turn we now to another apparent exception — the 

 modern horse. Comparative anatomy affords us 

 some very interesting information concerning the 

 fore-limb of the horse. It teaches us — as no one 

 who has looked into the matter disputes — that 

 what we call the knee of the horse is really its 

 wrist. Its " cannon - bone " corresponds to the 

 middle one of the five bones (called metacarpals) 

 which constitute the skeleton of the palm of the 

 human hand. The three bones which the veteri- 

 nary surgeon knows as the " pastern," the " coronary," 

 and the " coffin " bones, are strictly homologous with 



