CHAPTER XLII 



THE EVOLUTION OF THE PRIMATES AND MAN 



The Primates originated from a stock related to the Insectivora 

 probably in Cretaceous times. Plesiadapis, from the Early 

 Eocene, had characters in common with the Insectivora and 

 the Lemurs, which are the lowest Primates. The characteristic 

 of the higher Primates is that the bony bar separating the orbit 

 from the temporal fossa is complete ; or in other words, the 

 eye-socket is round and protected all round by bone. At the 

 same time, both eyes look more or less forwards so that their 

 fields of vision overlap and may coincide (stereoscopic vision). 

 There are five fingers and toes, and the first digits are opposable 

 to the others, except in the case of the first toe of man. This 

 opposability makes the limbs efficient grasping organs, and is 

 evidence for the fact that the early Primates lived on the 

 branches of trees. It will be seen in the sequel that this arboreal 

 habit had consequences of the highest importance in the 

 evolution of the Primates . Lastly , the most important character 

 of all in the Primates is the great development of the neopallium 

 in the cerebral hemispheres. 



In the Eocene the fossil Notharctus is found, representing 

 the earliest member of the group of the Lemuroidea. It was 

 very generalised, for whereas the primitive dental formula in 

 mammals is i| , c \ , p| , m| , that of Notharctus was i| , c \ , pf , mf . 

 From forms of this type the Lemurs must have descended. 

 The Lemurs alive to-day are nearly restricted to Madagascar, 

 though a few occur in Africa, Ceylon, and Malay. They are 

 fairly primitive animals, but show certain specialisations which 

 rule them out from the main line of Primate evolution. Among 

 these may be mentioned the peculiar procumbency of the 

 incisors of the lower jaw, with which they comb their fur. 



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