GREGORY: XOTIIARCTUS, AN AMERICAN EOCENE PRIMATE 



71 



culate, pentadactyl inammals with short hands and feet. They had powerful jironators, flexors, su|)i- 

 nators, extensors, brachialis anticus, pectoralis, deltoid, and scapular muscles. 



(2) They could i)rol)ably climl), dig, run, and swim, Init not in the s]iecialized ways of their remote 

 descendants. 



(3) Those which were ancestral to the creodonts and certain other Paleocene ordei-s were i)robal:»ly 

 small animals, perhaps not as large as a common opossum. 



(4) The Mesozoic ancestors of the primates were among the ^'ery small arboreal J'orms and were 

 of insectivorous-frugi^'orous habits. Even as late as the Lower Eocene, after the primitive primates 

 had become differentiated into several families, they were still of very small size; but in one phylum, 

 the Notharctinae, they increased rapidly in size in ascending levels, finally becoming about as large as 

 an Indris. 



(5) The ancestral stock, rejiresented to some extent by the Menoty])hla, i-emained small and indiffei"- 

 ently adapted to arboreal life. 



(6) The progressive lemuroid stock acquired primitive primate characters, which all relate, in the 

 locomotor apparatus, to adaptations for perching and leaping among the branches. 



The humerus of Notharctus differs from tliose of all other primitive mammals and resembles those of 

 the Eocene Adapinse and some modern lemurs in the following characters (Plate XXVH; Figs- 6, 7): 



(1) The delto-pectoral crest is not V-shaped and does not end below in a raised pointed ti]). It is^ 

 on the contrary, a low delicate crest with a thin edge, which i-uns down gently into the more 

 or less flattened cylindrical shaft. 



(2) On the inner side of the delto-pectoral crest opposite the tulierosity for tlie teres major is a more 

 or less vertically extended, shallow, oval fossa for the tendon of the latissinuis dorsi muscl(>. 

 (Plate XXVIII.) 



(3) The supinator crest extends much fvn-ther up the shaft than do those of the Menot3^phla and 

 Eocene Rodentia and it is relatively wider transversely than those of the Creodonta. It is 

 not curved so sharply backw^ard as are those of the primitive Taligrada, Edentata, Rodentia, 

 Insectivora. (Plate XX\TI.) 



(4) The great tuberosity is relati\'ely smaller than it is in primitive creodonts, taligrades, edentates, 

 rodents, insectivores, and Menotyphla. (Plate XXVII.) 



(5) The entocondylar process is relatively smaller than that of other Paleocene and Eocene mammals, 

 this implying that the pronator radii teres, and flexor muscles were less robust than in primitive 

 unguiculates. This is doubtless correlated with the presence of nails rather than claws. (Plate 

 XXVII; Fig. 5.) 



(()) The trochlea humeri is pi-ovided with a low external lip wliich tends to separate it fi-om the cai)i- 

 tellum, whereas in other Eocene mammals, except the Menotyphla, capitellum antl trochlea 

 are entirely confluent. This difference is correlated with differences in the noi-mal pose of the 

 I'adius and idna. In the other Eocene mammals the forearm is habitually pronated so that 

 the low' coronoid process of the ulna articulates with the iimer lip of the trochlea. In sucli forms 

 the head of the radius is extended transverseh', the <'apitellujn is less ball-like, and there is no 

 outer lip on the trochlea. In the primates, on the other hand, in conseciuence of their jjerching 

 and climbing habits, the ami is more often partlv supinated. This rotates the shaft of the ulna, 

 so that the large coronoid jirocess now presses against the outer part of the trochlea; hence, 

 an outer hp is developed on tlie troclilea while the imier li]) is much lower than in animals with 



