222 



GREGORY: NOTHARCTVS, AN AMERICAN EOCENE PRIMATE 



in minor details from those of existing lemurs; that is to say, the hands and feet were specially adapted 

 for grasping and clinging to the branches of trees. In the hind feet the first digit, or hallux, is very large 

 and normally set off at nearly a right angle from the other digits; its distal phalanx is flattened for the 

 support of a broad nail and at the proximal end of the first metatarsal is a large, inwardly projecting 

 process, for the attachment of the tendon of the peroneus longus muscle. The whole form of this digit 

 implies that the flexors and adductors of the hallux were at least as powerful as they are in the modern lemurs. 

 As a whole the hind foot, which is well adapted for both leaping and grasping, differs from that of Lemur 

 chiefly in having the metatarsals shorter and stouter, the proximal phalanges elongate. In man, on the 

 contrary, the foot has become adapted for terrestrial bipedal progression, the great toe having become 

 parallel to the other digits, the instep arched, the phalanges much shortened, the toes extended and the 

 foot planted firmly on the ground; so that the chief vestiges of ancestral arboreal habits are the great 

 size of the first digit, the strong dev^elopment of the flexors, adductor obliquus and transversus muscles 

 of the hallux and the presence of flat nails on all the digits. 



The hand of Notharctus, so far as preserved, appears to be in the main like that of modern lemurs 

 and to be adapted rather for tightly clinging to the branches than for the manifold use of the hand that 

 is attained in man. The scapula and clavicle are as in lemurs. The humerus, while nearest to that of 

 Lepilemur among recent primates, is remarkable for its shortness and width, for the emphasis of the 

 delto-pectoral crest, of the external epicondylar crest and of the entocondylar projection, all this implying 

 powerful climbing muscles. The radius resembles that of Lemur except that it is shorter; its subcircular 

 head shows that Notharctus had the power of supinating the forearm, which is a first requisite for a climb- 

 ing animal and a heritage of all primates. In the inan-anthropoid grou]) this power has been developed 

 to completion. 



The vertebrae of Notharctus are closest to those of Lemur; their detailed conformation implies that 

 the backbone as a whole was usually held in a more or less horizontal position rather than in the sitting 

 posture so often assumed by the higher primates. The cervical vertebrae are relatively elongate, in con- 

 formity with the Lemur-like form and pose of the skull; the dorsal vertebrae are small, this implying a 

 relatively small thorax. The lumbar vertebrae have elongate, vertically shallow centra with large para- 

 pophyses and f orwardly directed neurapophyses, as in climbing and leaping mammals, especially the lemurs, 

 whereas in the erect Homo and other primates which sit upright the lumbar centra are short and wide, 

 the parapophyses are smaller and spring from higher up on the sides of the vertebrae and the wide neura- 

 pophyses are directed more or less backward. All these details of the lumbar vertebrae imply a develop- 

 ment in Notharctus of the psoas, ci[uadratus lumborum, erctor spinae, and other muscles of the lumbar 

 region similar to that of animals which leap on all fours. The detailed conformation of the sacral, coc- 

 cygeal, and caudal vertebrae of Notharctus shows that the muscles for raising and lowering the tail and for 

 moving it laterally were essentially the same as in Lemur only less robust, and that it was not a prehensile 

 tail such as that of the typical South American monkeys. 



The pelvis likewise offers a wide contrast to that of Homo and of all the Anthropoidea, a contrast 

 which is expressive of the wide difference in mode of locomotion and habitual pose of the body. The 

 ischial tuberosities are not expanded as they are in Homo and in all other primates which habitually sit 

 upright. The narrow blade of the ilium differs from that of Lemur chiefly in its shortness and in the depth 

 of the fossa for the deep gluteal muscles, whereas in the erect Homo the blade of the ilium is much widened 

 for the support of the heavy viscera and robust abdominal muscles and for the insertion of the spreading 

 muscles of the buttocks. Very characteristic of Notharctus and the lemurs is the presence of a strongly 

 marked protuberance on the anteroventral border of the ilium in front of the acetabulum. This is homo- 



