224 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



The palate of Notharctus is long and narrow whereas in many of the higher primates it becomes short 

 and broad. The upper dental arch is pointed in front instead of arched or convex. The small pterygoid 

 fossae of Notharctus are most nearly represented in the modern lemurs but are variously widened in the 

 Old World monkeys and in the man-anthropoid groups, perhaps in correlation with an increase in size 

 in the internal pterygoid muscles. The descending or pterygoid plate of the alisphenoid of Notharctus 

 is very large and extends backward and outward to the glenoid region and to the auditory bulla, as it 

 did in primitive placentals of the Eocene and as it still does in somewhat reduced form in certain lemurs; 

 whereas in the higher primates it is generally separated from the glenoid region and from the auditory 

 bulla by a considerable interval. In this feature the closest resemblance is with Adapis of the Eocene 

 of Europe. 



The auditory bullae of N^otharctus also afford a ready means of distinguishing it from the Man- 

 Great-ape group and from all other Primates except Adapis and the lemurs. The bullae consist of 

 hemispherical swellings, formed probably as a vesicular outgrowth of the petrosal, situated immediately 

 behind the pterygoid plate of the alisphenoid and internal to the glenoid region; they cover the small 

 auditory prominence of the petrous bone, and are continued anterointernally into processes which articu- 

 late with the basioccipital and basisphenoid. The ring-like tympanic bone was covered by the bulla. 

 All the construction in this region conforms to the plan of Adapis and the lemurs and is far more primitive 

 than the conditions seen in the auditory region of the New World monkeys, of the Old World monkeys 

 and of the man-anthropoid group. 



Notharctus differs from all apes and monkeys and even from all lemurs, except Adapis, in the short- 

 ness of the basioccipital segment. This is correlated with the much smaller brain-capacity and is in 

 harmony with the low, short brain-case. The position of the condyles, which face chiefly on the back 

 of the occiput instead of being more or less beneath the occiput, clearly shows that the head was not 

 bent at so sharp an angle with the neck as it is in man and many other Primates, but that it was held more 

 as it is in lemurs; the inclination of the basifacial to the ba&icranial axis was even less than it is in the 

 modern lemur and offers a wide contrast to the sharply inclined basifacial axis of New World monkeys, 

 Old World monkeys, great apes, and man. 



Mandible 



The lower jaw of Notharctus is distinguished from those of modern apes and of man by its 

 greater length and slenderness and to a much less degree from that of Lemur by its greater depth and 

 robustness. The symphysis is fused in old individuals, a character that foreshadows the early fusion 

 of the symphysis in Man and all the Old World and New World Primates. The lower border of 

 the jaw is curved and the angle is produced into a long, broad, posterior process which is incurved below. 

 On the inner side of this process was inserted the internal pterygoid muscle, which had its origin on the 

 elongate pterygoid plate of the alisphenoid and in the pterygoid fossa. This is very probably the primi- 

 tive condition for all primates. The form of the condyles and of the teeth show that the jaw was moved 

 obliquely from side to side in chewing. The mandibular condyles were rounder and less flattened than 

 those of lemurs, less transversely expanded than those of New World monkeys, great apes, and man. 



In this connection may be quoted Leidy's sagacious remarks in 1873 on the lower jaw and dentition 

 of Notharctus: 



In many respects the lower jaw of Notharctus resembles that of some of the existing American monkeys quite as much 

 as it does that of any of the living pachyderms. Notharctus agrees with most of the American monkeys in the union of the 

 rami of the jaw at the symphysis, in the small size of the condyle, in the crowded condition of the teeth, and in the number 



