26 PROCEEDIlSrGS OF THE ISTATIONAL, MUSEUM. vol.63. 



AlouaUa and Cehus; and, so far as I have observed, does not occur in 

 any modern lemurs or in the Old World anthropoids. 



The clavicle of Notharctus, represented by the "medial half," is 

 described as similar to that of Lemur mongoz, but, according to 

 Gregory, it has a "stouter, less compressed shaft and a less expanded 

 facet for the sternum." Gregory also stated that this portion of the 

 clavicle is nearly straight. These features are true also of this por- 

 tion of the clavicle in AlouaUa. In this genus the medial portion is 

 almost straight and is as round in cross section as in Notharctus. 



In discussing the humerus of Notharctus, Gregory has said (p. 76) 

 that "the nearest structural resemblances are to be found among 

 the Lemuriformes, especially among the Adapidae and Lemuridae. 

 Hence the humerus of Notharctus, as well as the great majority of all 

 other elements of the skeleton, is plainly lemuriform, or better, in a 

 prelemuriform stage of evolution." This statement, applied to a com- 

 parison of Notharctus with the Old World anthropoids and man, is in 

 genera] quite true, as was clearly demonstrated by Gregory, but when 

 the South American monkeys and the African continental and Asiatic 

 lemurs are considered, the "lemur" characteristics seem not so well 

 founded, and his conclusion of a "prelemuriform stage" does not 

 seem to follow, unless we are to consider the modern Madagascar 

 lemurs to be still in the prelemuriform stage. In fact, modifications 

 noted in the humerus of the living South American group seem to 

 have a definitely closer connection with the Notharctid type than do 

 those of the modern true lemurs. For example, although the shaft 

 is greatly lengthened (an obviously modern specialization), the sig- 

 moid, or S-shaped contour of the humerus of Alouatta, viewed from 

 the side, is almost as marked as in Notharctus, and as fully or even 

 more marked than that of Lemur cattus, while the deltoid ridge and 

 supinator crest are almost as strongly prominent as in those of Lemur. 

 In Hapale the deltoid ridge is more strongly produced than in Lemur 

 cattus. In Cehus and Aotus this element is more reduced. As noted 

 by Gregory, in several of the South American monkeys the entepi- 

 condylar foramen is as prominently present as in Notharctus. Com- 

 paring further, the heads of the humeri in the various Platyrrhine 

 are also but little modified beyond the stage observed in Notharxtus, 

 those of Cehus and Hapale being closely similar. That of Alouatta is 

 slightly more compressed and less "globular" in form, while in all 

 the inclination and direction of the head is directly toward the back 

 of the shaft, as in Notharctus, and the bicipital groove is relatively 

 wider and shallow. An apparently important character, not noted 

 by Gregory, in which the Notharctus humerus differs from all lemurs 

 and resembles the Anthropoidea, is the angle which the base plane of 

 the ball portion of the head makes with the long axis of the upper 

 shaft. In Notharctus this angle is about the same as in the South 



