No. 536] ADAPTATIONS OF THE PRIMATES 



183 



Those in South America quickly differentiated by the 

 loss of the first premolar, making a dental formula of 

 %, Viy %, % = 36. With this also goes a deepening of the 

 ramus of the lower jaw, a shortening of the face, and a 

 tendency to develop the occipital region so that it over- 

 hangs widely the foramen magnum. This group of 

 forms is termed the ( Vbida\ On becoming successfully 

 adapted to the South American continent and during the 

 long isolation of that area, these early forms have 

 gradually adapted themselves in various directions, often 

 paralleling old world types. In size they have developed, 

 the largest forms having a body of 27 to 28 inches in 

 length, and legs as long, making a height of 414 feet, 

 which is a good-sized monkey. They have always re- 

 mained arboreal with opposable thumbs and a prehensile 

 tail; but they vary from the slender spider monkeys to 

 the robust and powerful woolly monkeys {Lugnthrlr). 

 From the above has been specialized the family of mar- 

 mosets (Hapalidas), by the loss of the last molar (mak- 

 ing the dentition %, 1 ,, :! . ; . =32), by the development of 

 a broad nasal septum, the loss of the prehensile character 

 of the tail and opposability of the thumb. 



The southwesterly wave of migration crossed the Beh- 

 rings connection and moved down the easterly part of 

 Asia across the Indo Madagascar isthmus and into 

 Africa. This isthmus or series of islands sank at or 

 toward the end of the Eocene, leaving lemurs stranded 

 all along the area occupied by the isthmus. Those on the 

 islands and especially on Madagascar have remained 

 very much as they were, adapting themselves in minor 

 ways, but being always arboreal. Some peculiarities 

 must have developed very early for they are common to 

 the group, like the having of the lower incisors project- 

 ing forward (proclivous), the lower canine small and 

 like an incisor, while the first premolar acts as a canine 

 tooth. Then the fourth digit of the hand is longest, and 

 the second one of the foot is clawed instead of having a 

 nail. In this lemur group we know only the immediate 



