GREGORY: NOrHARCTUS, AN AMERICAN EOCENE PRIMATE 



145 



some of the deep jaws (A^. osborni) have small canines and appear to belong to females while other deep 

 jaws (N. venticolus) bear large canines and apparently belonged to males. 



The condyle is best preserved in N. osborni (Amer. Mus. No. 11466), N. tyrannus (Yale Univ. Mus. 

 No. 12151), and A^. crassus (Amer. Mus. No. 12588). As seen from above it is bean-shaped, with the 

 concave side turned backward; the inner end is produced downw^ard and backward and in A^. crassus 

 this downward prolongation is very pronounced, so that much of the articular surface may be seen from 

 the rear; the whole condyle is broadly convex both transversely and anteroposteriorly. This shape of 

 the condyle is correlated with the shape of the glenoid cavity and postglenoid process (see below, p. 159). 

 The mandible was capable of very free motion in the glenoid fossa (as may be seen in the type of A^. 

 osborni and in A'', crassus) and could be shifted forward, when special pressure was exerted upon the canines, 

 incisors and premolars, as well as inward or outward, as in lateral movements of the mandible (see below, 

 p. 148). 



The condyle of Adapis parisiensis (Amer. AIus. No. 10007) differs from that of Notharctus in being 

 extended transversely, without the backward and downward turning of the inner moiety; it is also flatter 

 above. It is more analogous with that of Lemur and was probably less freely displaced laterally and 

 anteroposteriorly. (Plate XXXIX.) 



The coronoid process is well preserved only in N^. pug nax (Amer. Mus. No. 11480) and Af . te7iebrosus 

 (Yale Univ. Mus. No. 12151). It is very large and high with a strong anterior border, defining the 

 insertion area of the temporal muscle, and a nearly straight and vertical posterior border. It differs 

 from that of Adapis in not being sharply recumbent and in having the posterior border straight instead 

 of concave. The temporal insertion areas on the inner and outer sides of the coronoid process were 

 consequently not so wide inferiorly as in Adapis but were more extended vertically. The areas for the 

 masseter internus and masseter externus, on the side of the ascending portion below the temporal area 

 were, on the whole, much less extensive than in Adapis parisiensis, since the whole region of the angle 

 was less expanded. The masseter fossa is sharply defined anteriorly by the ridge that runs down from 

 the coronoid process. As in other mammals with stout malars the masseter doubtless bulged prominently 

 below, and pressed the border of the jaw inward, this causing the characteristic concavity of the lower 

 border behind the swollen middle part of the ramus, which is seen in many Eocene mammals and some 

 modern carnivores and insectivores. This peculiar concavity of the lower border is even more pronounced 

 in Adapis which doubtless had a much swollen masseter. The lower border and adjacent inner surface 

 of the jaw in front of the concavity above mentioned is shghtly roughened in some specimens; this may 

 very well mark the insertion area of the digastric muscle, which in Propithecus, Lemur and many other 

 mammals is inserted in this region.^ In Adapis a fossa on the inner side of the jaw above and in front 

 of the masseter concavity is provisionally identified by Leche and by Stehlin (1912, p. 1221) as probably 

 for the insertion of the mylohyoid, but to the present wTiter this area, by comparison with Propithecus, 

 seems much more likely to mark the insertion of the digastric, the mylohyoid area being probably above it. 

 (Plate XLI.) 



The angle of the jaw is well preserved only in A^. venticolus (Amer. Mus. No. 14655). It was not 

 widely expanded as in Adapis, but was of primitive lemuroid form, though wider than in most lemurs. 

 Externally it bears the lower part of the masseter area and internally it bears the well-defined lower 

 -fossa for the internal pterygoid muscle, flanked by a sharp crest above and by the rounded inturned 

 border below. It was the broken section of this partly inturned border, which is conditioned by the 



' See the dissections in Milne Edwards and Grandidier (1875) and in Cuvier and LauiiLlard ''Planches de Myologie." 



