GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



157 



shown in A^. matthewi, Amer. Mus. No. 13030, passes above the tubercle for the anterior tendon of the 

 masseter and runs obhquely upward, forward and inward toward the lacrymal, as in Adapts. The lower 

 part of the malar was deeply cleft into inner and outer laminae which embraced the thin zygomatic process 

 of the maxilla (Amer. Mus. No. 13030). The posterior zygomatic part of the malar is not known, but 

 it probably did not extend back to the glenoid (p. 159 below). 



Frontals 

 Text Fig. 54 



The frontals of Notharctus osborni are distinctly wider across the forehead than those of Ada-pis 

 and the orbits are larger. In Notharctus venticolus (Amer. Mus. No. 14656), however, the frontals are 

 very much narrower. The superior surface of the frontal, above the orbit, shows in A^". venticolus a moder- 

 ate swelling (above the fore part of the frontal sinus), behind which is a wide shallow depression. This 

 condition is suggested in A'', osborni, and seems to be indicated in varying degrees in different skulls of 



Fig. 54. Skull of Xofharctus os- 

 horiu. Amer. Mus. No. 1 1466. Nat- 

 ural size. Fig. 55. Skull of Adapl.s iiKujnus var. 



Iccnhardti. After Stehlin. Natural size. 



Adapis figured by Stehlin. The temporal crests of the frontals behind the orbits are further separated 

 in Notharctus osborni than in most forms of Adapis, but in A^". venticolus this part of the skull is narrower. 

 The frontal sinus was well developed (A^. venticolus); the opening for the cribriform plate was large. As 

 in Adapis the frontals did not extend far back over the top of the brain (A^. venticolus). The sides of the 

 interfrontal suture on the cerebral surface are raised into a low ridge corresponding in position with the 

 interfrontal sinus. The lower border of the frontal has a wide contact with the lacrymal. The orbital 



