MAK,'S RELATIVES: THE PRIMATES 



473 



openings. Such a bar is present in all primates. Beneath this bar in the tarsioids 

 and anthropoids, a thin sheet of bone is formed which completely closes off the 

 eye socket at the rear — a structure found in no other animals. Presumably the 

 complete bony socket gives better muscle attachment and support for the eyes in 

 their forwardly rotated position and 

 prevents disturbances of vision caused 

 by movements of the jaw muscles. 1 



The lemurs. These are the sim- 

 plest of the primates, recognized as 

 fossils from the Paleocene and 

 Eocene of Europe and North 

 America. They survive today chiefly 

 on the island of Madagascar, where 

 they have been protected by isola- 

 tion. Typical lemurs are small four- 

 footed arboreal animals, somewhat 

 squirrel-like in appearance, with 

 fluffy hair and a long bushy tail. 

 In structure they are only a little 

 more advanced than their ancestors 

 the tree shrews. The muzzle is long 

 and pointed, the teeth suggest those 

 of insectivores, the eyes are directed 

 outward and lack a complete bony 

 socket, and although some of the 

 toes have flat nails, certain toes 

 typically have clawlike ones. The 

 placenta is very simple; projections 

 inserted into the uterine wall occur 

 in scattered groups over its surface 

 and are pulled free at birth. Some 

 of the early Cenozoic lemurs 

 appear to be transitional to the 



Fig. 29.2. The ruffed lemur of Madagascar, 

 Lemur varius. {Courtesy Zoological Society 

 of Philadelphia.) 



tarsioids, and the latter were evidently derived from some lemur stock. 

 The tarsioids. This group is represented today by a few species of 

 the highly specialized genus Tarsius, a relict type found in the East 

 Indies. These tarsiers are small, nocturnal, arboreal creatures, with 

 ratlike tail and furred body. The hind legs are specialized for hopping, and 

 all the toes are very long and slender, with flattened clinging disks at the 



1 A very good and complete account of the changes that have occurred during the 

 evolution of the primates is to be found in Hooton's book, Up from the Ape, The 

 Macmillan Company, New York, 1947. 



