88 



GREGORY: XOTHAHCTUS, AN AMERICAN EOCENE PRIMATE 



small and that possibly the newborn young may have had the brain-case less expanded than that of higher 

 pri] nates. 



The pelvis of Propiihecus is slightly modified from the N^otharctus type in the wider di\'ergence of 

 the ilium, in the prolongation of the anterior inferior process of the ilium, and in the relative shortening 

 of the ischia. Thus Propithecus is a little more specialized for leaping. In all palseotelic features of the 

 pelvis the agreement is remarkably close. (Plate XX VT.) 



The pelvis of Chiromys is also slightly specialized away from the Notharctus type through the nar- 

 rowing and elongation of the ilium, but is fundamentally similar to it, and contrasts widely with the pelvic 

 types of the New World and Old World monkeys. 



The peh'is of the Old World monkeys is much nearer to the New Workl type than to that of lemurs. 

 The iliac blade is progressively widened and e\'ei-ted, finally attaining a very wide expansion in man; 

 this is no doubt correlated with the habit of sitting upright, with the relatively heavy abdomen and with 

 the widening of the gluteus medius and minimus. The anterior inferior spine of the ilium is confluent 

 with the anterior expanded border; in correlation with the sitting habit the ischial tuberosities are widely 

 expanded and evei'ted. 



In man the A-ery widely expanded and everted blade of the ilium is associated with the fully ei'ect 

 posture^ l)oth in sitting and walking; the capacious false pelvis affords support to the voluminous abdomi- 

 nal vis('(M-a, ihv areas for the gluteus medius, gluteus minimus and iliacus are much increased, the lines 

 of insertion of the external trans\-erse and oblique abdominal muscles on the crest of the ilium are greatly 

 widened; the eversion of the anterosuperior spine of the ilium is associated with a more \'ertical pull of 

 the tensor vagimi; femoris, of the sartorius, and of the ilio-femoral ligament, in standing and i)rogressing. 



Comparative Measurements of the 



'elvis 









Nothard us 



Nothard ux 



Lemur 



Ccbus 





osbonii 



osbonii 



mongoz 



Injpokucus 





No. 11466 



No. 11479 



No. 31254 



No. 14017 



Total Length from anterior tip of ilium to isehial tuberosity 





7.3. 



81.. 5 



S3. 



Length of Ilium from mickile acetabulum to anterior dorsal tip 





48.. 5 



.30. 



.37. 



Length of Ischium from middle acetal)uhiin to iscliial tul)erosity 





2.3 . .3 



24..-) 



20.5 



Width of Ilium, anterior end 





19. 



18..") 



19. 



IHac Index (width/ length) 





.39 



.30 



:!() 



Anteroposterior Diameter of Acetabuhuu 



14..') 





11. 



12 



Anteroposterior Diameter of Tiiyroid Foramen 





13. 



10, 5 



17. 



llio-ischial Ratio 





1.90 



2.28 



2. 15 



These measurements emphasize the relative shortness in Notharctus of the ilium as compared with 

 the ischium, the large size of the acetabulum and the small size of the thyroid foramen or fenestra. 



Femur 

 Text Figs. 15, Hi 



The right femur is preserved in Notharctus osborni, No. 11474, and less completely in other specimens 

 of N. tyrannus and tenehrosus. They are, on the whole, close to those of Lemur mongoz, which are 

 only a little longer. It is surprising that while the humerus of the modern Lemur mongoz has become 



