68 



GREGORY: NOTIIAHCTUS, AN AMERICAN EOCENE PRIMATE 



p. 15) has recorded this condition in the indrisine lemurs and has noted that, although it adds greatly 

 to the power to flex the forearm, it makes it impossible to extend the lower arm fully. In the monkeys, 

 on the other hand, says Milne Edwards, the supinator longus much resembles that of man; it is inserted 

 only on the lower part of the humerus, is much more delicate than that of the Indrisina^, and does not 

 hinder the full extension of the forearm. 



That the forearms of Nothardus were incapable of extreme extension is also in agreement with the 

 fact that the olecranal fossa is very shallow while in the higher i:)rimates, which fully extend the forearm 

 and thus force the coranoid process of the ulna into the back of the upper arm, the olecranal fossa is much 

 deeper. 



In correlation with the bent i^osture of the arms is the fact that the delto-pectoral crest is much more 

 prominent than it is in the higher primates. The "Planches de Myologie" of Cuvier and Laurillard show 

 that in many of the lower mammals the deltoid extends further down the arm than in the higher primates. 



A very significant primitive character of the humerus of Nothardus is the fact that the moderate- 

 sized head is inclined chiefly toward the back of the shaft, as it is in many }irimitiA'e mannnals with bent 

 limbs, while in the anthropoid apes and man the head has become greatly enlarged on the inner side 

 and inclined toward the inner side of the shaft, because the habits of sitting upright and of walking either 

 upright or in a stooping position causes the elbows to be turned outward and the humerus to be rotated 

 inward so that when the arms are swinging freely the scajnila articulates largely with the internal part 

 of the head of the humerus, the rest l)eing covered by the caiisule. 



The same primitive quadrupedal jiosition of the hinnerus in Nothardus permits the lesser tuberosity 

 to be directed chiefly backward and upward, while in man antl anthropoids the frequent outward turn- 

 ing of the elbows and inward rotation of the head of the humerus has pushed the lesser tuberosity around 

 on to the front face of the humerus so that it is finally only separated from the greater tuberosity by a 

 narrow bicipital groove. 



In spite of all these primitive mammahan characte2's the humerus of Nothardus still exhibits a number 

 of DiACiNOSTic PRIMATE CHARACTERS. These may be conveniently exhibited by successive compari- 

 sons of the humerus of Nothardus with those of various Paleocene, Eocene, and other primitive mammals. 



Marsupials. The humerus of Didelphis may be taken as the primary type for the Polyprotodontia, 

 that of Phalangista as the primary type for the Diprotodontia. Both resemble that of Nothardus in 

 possessing a number of primiti^'e characters, such as an entepicondylar foramen, well-developed supi- 

 nator crest, etc., but both differ from it in several points, especially the following (Plate XXVII): 



(1) The supinator crest is more or less angulate at the upper end. 



(2) The delto-pectoral crest is more elevated at the lower end and is continued further down the 



shaft. 



(3) The humerus as a whole is shorter and wider with larger proximal end. 



Very probably these are primitive marsupial characters of the humerus and they may represent 

 a \-ery ancient and primitive arboreal stage following the therapsid stage of mammalian ascent. 



Creodonts. Many creodont humeri have been compared with that of Nothardus. They possess 

 all the primitive mammalian characters enumerated above but they differ from Nothardus in the fol- 

 lowing : 



(1) The massive flattened deltoid crest terminates below in a prominent deltoid eminence which 

 is wanting in Nothardus. 



