OBSERVATIONS OF THE AUTHOR 425 



in the weakening of the lower jaw, and especially in the characteristic 

 lemurid specialization of the incisors, canines, and anterior premolars — 

 a specialization which Notharctus had not assumed. 



The lower jaw of the earlier species of Notharctus has two important 

 primitive characters in common with that of modern Lemurs : First, the 

 two halves are suturally separate at the symphysis, whereas in the Anthro- 

 poidea, including the Xew World monkeys, or Platyrrhinse, and the Old 

 World monkeys, apes and man, or Catarrhinse, the opposite halves are 

 fused at an early stage of development ; secondly, the angle forms a long 

 backwardly projecting process for the insertion of the internal pterygoid 

 muscle, whereas in the Anthropoidea the angle is much expanded. The 

 lower jaw of Notharctus is also iiiore primitive than that of the existing 

 Lemurs in retaining erect canines and incisors. 



The upper incisors are of a very primitive compressed type, which 

 could give rise, witli slight modifications, to the upper incisors of the 

 existing Microcehus of the Jjemuridie, and in another way they resemble 

 the incisors of Adapis. 



The vertebral column is, on the whole, rather close to that of existing 

 Lemurs, considerably different from that of existing ISTew World Pri- 

 mates and widely different from that of Old World Primates. 



For example, the lumbar centra are elongate, with depressed ends, as 

 in Lemurs, while in the Anthropoidea the centra are short and wide and 

 the ends are vertically thicker. Again, the wide parapophyses of the 

 lunibars are similar to those of Lemurs. 



Tlie pelvis is decidedly Lemur-like in the lyrate form of the ilia, in 

 the prominence of tlie ])rocess for the rectus femoris muscle, and in the 

 non-expansion of the ischia. The remaining limb bones and the hands 

 and feet are strikingly like those of Lemur, the chief differences being 

 that the metapodials and the humerus are decidedly short — a primitive 

 character. 



CONCLUSIONS 



Tn conclusion, the type of skeleton which is represented in Notharctus 

 appears to l)e considerably nion' [)rimitive than that seen in any later 

 Primate ; it has been transmitted, with minor changes, chiefly of propor- 

 tions, to modern Lemurs, while very distinct traces of this skeletal pat- 

 tern are retained in varying degrees by the Hapalidai and Cebidae. From 

 the skeletal pattern of the Old Woild Primates, however, it is separated 

 by a wide structural hiatus. 



