THE LAST STAGES IN THE GENEALOGY OF MAN 177 



stock started from some point in the ungulates. I liave manifested 

 my repugnance to supposing such an origin, which appears mon- 

 strous. But while this repugnance is legitimate when we have 

 regard to recent species — the extremities evolved from the branch 

 — it is less so when we go back to the trunk before the specializa- 

 tion of the ungulates had become as pronounced as it is now. It 

 must be said that nothing is impossible in nature ; that things the 

 least probable when we look at the outcome are realized by the 

 most unforeseen processes, the most tortuous roads. What selec- 

 tion by the hand of man has done for pigeons is found done in 

 nature by means the laws and mechanism of which are invisible 

 to us, and which we can only denominate chance. 



There is one objection to the descent of man from the ape 

 which I have entertained, and which comes to the suyjport of M. 

 Vogt's thesis. As I have previously said, the primordial type 

 of the mammalia has four limbs, the destination of which is 

 already written out as far back as we can go ; all four fitted to 

 walking, but the fore-limbs adapted besides to serve as organs of 

 prehension, while the hinder ones are essentially organs of sup- 

 port and walking. This double specialization goes back to the 

 reptiles, not to speak of the dinosaurians, with which it is very 

 marked. Some amphibians present traces of it. With the most 

 ancient mammalia which are known in all their parts, like the 

 Phenacodus iDTimc2vus of the Lower Eocene of Wyoming Territory, 

 the fore-limb is well characterized as an organ of prehension and 

 the hinder one as for walking. The humerus is articulated with 

 a narrow glenoid cavity at the upper outer angle of the omoplate, 

 so as to permit the freest motions in different directions ; the 

 radius is mobile on the cubitus, around which it performs the 

 turning movement required by the function of the hand ; the five 

 fingers are spread out, the thumb is turned more on its axis as if 

 to permit opposition, and the hand continues in a straight line 

 with the forearm. On the other hand, the femur is united, as 

 with us, to a massive pelvis ; the articular surfaces of the knee, 

 the knee-pan, and the two immovable bones of the leg, are just 

 what the exclusive function of locomotion requires; the foot is 

 plantigrade, with a prominent heel and close toes, and is articu- 

 lated perpendicularly by its arch with the leg, as in man. With 

 another contemporary animal of the same bed, the Corypliodon, 

 of which I have only representations of the foot and hand, but 

 those whole, to judge by, these two organs present more resem- 

 blance, the foot being a little like a hand, but the differentiation 

 is nevertheless made. 



This specialization or differentiation has reached its maximum 

 in man, no other animal showing it in equal degree. In the bird 

 the upper limb has become a wing, that is, a function of locomo- 



TOL. XXXIV. — 12 



