436 Wortman — Studies of Eocene Mammalia. 



a type of cerebral circulation which might easily have passed 

 into that of the Antliropoidea, through the suppression and dis- 

 appearance of the stapedial branch of the entocarotid ; but, as 

 we have already seen, this character is shared by the Podentia 

 and probably by other groups as- well. At the same time it 

 does not furnish a type of cerebral circulation from which that 

 of the lemurs could have been evolved. 



The greatest difficulty in the Avay of deriving the Primates 

 from any form or forms of the Insectivora at j^resent known 

 consists in the total lack of prehensile powers of the manus 

 or pes. Any group which is placed ancestral to the Primates 

 must of necessity be one in which some distinct approach to 

 this condition is made, since its possession is one of the chief 

 requisites of fundamental importance. For this reason, if for 

 no other, the modern types, at least, of the Insectivora, can not 

 be looked upon as the forerunners of, or as more than very 

 distantly related to, the ancestors of the Primates. 



"With the single exception of Lophiomys among the Poden- 

 tia, the only other living mammals which exhibit prehensile 

 extremities are found among the Marsupials, and the evidence 

 points very conclusively to the fact that all of them, even those 

 with highly modified limbs for terrestrial progression ( as the 

 kangaroos ), are descended from ancestors with grasping hands 

 and feet. It is therefore not beyond legitimate supposition to 

 assume the existence of a very considerable group of ancient 

 Metatherians living within the Arctic Circle during Cretaceous 

 time, whose manner of life had already become arboreal. If 

 such a group did exist, it is far more likely that the Primates 

 were derived from it rather than from the Insectivora or any 

 other group now living. Future research and discovery in 

 these regions will alone settle the correctness or incorrectness 

 of this hypothesis, and until such discoveries are made we 

 must be content with the results of speculation. 



[To be continued.] 



