158 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



lamina of the frontal (N. oshorni) was in contact with the orbital plates of the palatine and of the orbito- 

 sphenoid, and probably also with the alisphenoid. It was apparently excluded from contact with the 

 squamosal by the parieto-alisphenoid contact. Similar relations of the frontal were observed by Stehlin 

 in Adajns magnus (1912, p. 1252). 



Parietals 

 Text Fig. 54 . 



The coronal suture is not clearly defined except in a skull fragment referred to A'', oshorni (Amer. 

 Mus. No. 11474), where enough of the fronto-parietal suture is preserved to show that the fore part of the 

 parietals were overlapped by the constricted interorbital part of the frontals, as they are in Adapts. 

 The mid-parietal expansion is much more pronounced in the female skull of N. oshorni (Amer. Mus. No. 

 11466) than in the old male of N. venticolus (Amer. Mus. No. 14655) which has a very narrow brain-case 

 and a long high sagittal crest. In A^. crassus this crest becomes very high. This is less convex antero- 

 posteriorly than in Adapts. As in Adapts the parietal crest and the parietal itself are continued back 

 to the occiput, the supraoccipital not being exposed on the top of the skull. Anteriorly, at the back of 

 the orbit, the parietal appears to be in contact with the frontal, orbitosphenoid and alisphenoid. The 

 sides of the parietal in A^. oshorni are swollen, but much less so in N. venticolus and A^. crassus. By reason 

 of the relatively small size of the brain the parietal convexity of Notharctus, as well as of Adapis, is some 

 distance behind the postorbital rim and there is consequently little if any tendency to close the orbit by 

 a posterior partition. Laterally the parietal is bounded by the long irregular parieto-squamosal suture 

 which begins near the parieto-aUsphenoid contact and ends at the lambdoidal crest, after passing through 

 the parieto-squamosal foramen, as in Adapis. 



Squamosals 

 Text Figs. 48, 49, .54, .58 



This element is known chiefly from the type of A^. oshorni and from a large fragmentary skull of 

 A^". crassus (Amer. Mus. No. 12567). Its general relations are the same as in Adapis and many other 

 primitive primates. On the anterior part of the squamosal there is a sharp horizontal ridge which is 

 continuous with the anterior edge of the glenoid region; this ridge separates the area of the temporal 

 muscle from that of the external pterygoid. Stehlin (1912, p. 1200) states that in Adapis this ridge 

 extends forward across the alisphenoid to the orbitosphenoid and the same is true in Notharctus (N. 

 oshorni). There is a wide difference in the glenoid region between the female skull of A'', oshorni and the 

 large male skull of A^. crassus (Amer. Mus. No. 12567). In the former the glenoid fossa is shallow, the 

 postglenoid process is delicate and the entoglenoid process is low. In the latter the glenoid fossa is deeply 

 concave, the postglenoid process is robust and the entoglenoid process is represented by a sharp ridge. 

 Again in N. oshorni the entoglenoid process and the pterygoid flange of the ahsphenoid were separated 

 only by a narrow fissure, while in A^. crassus these parts, except in the rear, were separated by a portion 

 of the squamosal which is about 5 mm. wide at the front end. In Adapis the glenoid region is flatter 

 and there is little indication of the entoglenoid ridge; this region, however, is in contact with the ptery- 

 goid flange of the alisphenoid as in A^. oshorni. The tip of the postglenoid process is roughened in Noth- 

 arctus as well as in Adapis, probably by the posterior slip of the masseter externus.^ In both A^. oshorni 



1 See the dissection of Propithecus diadenia in the Memoir of Grandidier and Mihie Edwards. (Hist. Physique Nat. et Politique 

 de Madagascar, IX, Tome IV, Atlas, PI. lv.) 



