146 



Gregory: notharctus, an American eocene primate 



bulging of the masseter and by the insinking of the pterygoid fossa, which misled Marsh into attributing 

 an "inflected angle" to the jaw. But the inflection, such as it is, is widely different from that which is 

 characteristic of the marsupials. In Adapts the lower fossa for the internal pterygoid is not fundamentally 

 dissimilar to that described for Notharctus, but is wider dorsoventrally and less produced backward. 



Fig. 43. Lower jaws of Notharctun pugnax. Amer. Miis. Xo. 1 1480, Middle Eocene (Upper Bridger), and N. venticolus, 

 Amer. Mus. No. 14655, Lower Eocene (Wind Ri\er). Lateral view. Natural size. 



T 



Fig. 44. Lower jaw of Add pis- pdri.s/in.vi.s. .Vt'ter Stehlin. Natural size. 



The upper fossa for the internal pterygoid in both Notharctus and Adapts lies below the ridge forming the 

 lower border of the temporal area. The inturning of the lower border of the jaws, beneath the lower 

 internal pterygoid fossa, is very pronounced in certain old individuals of A. parisiensis (Amer. Mus. Nos. 

 10014, 10010, 10012). Such an inturned border has been acquired independently in many placental 

 mammals and is quite different in form from the true inflected angle of the marsupials. 



The external pterygoid muscle of Notharctus was probably inserted in a small fossa just below and 



