GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



209 



increase in the facial exposure of the lacrymal in Lemur ' and the consequent readjustments in the surround- 

 ing bones, the chief differences in the facial region are as follows. 



(1) The premaxillary in Lemur is less extended upon the face in side view; this, however, is less 

 apparent in Microcebus, Chirogale and Atililemur, which have well-developed incisors, a pro- 

 jecting muzzle and therefore relatively large premaxillse. 



(2) The general plane of the orbits in Lemur is more vertical, so that they are less directed upward. 

 This is apparently conditioned by the fact that in Lemur and Lepilemur the forehead is higher. 

 In Chirogale which has a low forehead the orbits are more widely seen in the top view of the skull. 



(3) The suborbital portion of the malar in Lem,ur is less extended vertically than in Adapts. This 

 is associated with the great expanses of the areas for the masseter in Ada pis and with the partly 

 retrogressive development of these areas in typical Lemuridse. 



The more striking differences in the brain-case are nearly all related to the great expansion of the 

 brain in the modern forms which has conditioned such necessary readjustments as the more or less wide 

 exposure of the fused interparietals and supraoccipital upon the top of the occiput. This exposure is 

 comparatively slight in the primitive Myoxicehus simus and attains its maximum in Lemur. 



The frontals in Lemur are produced backward above the cerebrum, so that the coronal suture is 

 nearly transverse. In the primitive Myoxicehus simus, on the other hand, the coronal suture is almost 

 V-shaped. In Adapts, on the other hand, the frontals are remarkably small (Stehlin, 1912, p. 1194) 

 and take very little part in covering the cerebrum, but cover chiefly the olfactory chamber and the orbits. 

 This is surely a primitive character which Adapts shares with many other Eocene mammals. 



Another apparently primitive character of Adapts is that the floor of the brain-case is nearly parallel 

 to the palate (Stehlin, 1912, p. 1198) while in Lemur it is considerably inclined toward it. In Adapis 

 also by reason of the small size of the brain the plane of the foramen magnum forms a somewhat sharper 

 angle with the base of the cranium than it does in Lemur. 



The temporal flange of the squamosal is well developed in Adapis, and extends higher up on the side 

 of the brain-case than in Lemur, in which both the temporal and the zygomatic portions are feebly devel- 

 oped. In Adapis the crest of the zygomatic process above the auditory meatus and the root of the process 

 are inflated or pneumatic. In Lepilemur some of this condition remains, but in Lemur the air cells of 

 this region as shown in several sections are of small size. The mastoid of Adapis is thoroughly pneu- 

 matic, like that of Lepilemur, but in Lemur the occipital surface of the mastoid while much expanded is 

 thin and deflated. The lower side of the mastoid bears in Adapis an S-shaped groove, no trace of which 

 remains in Lemur or in Lepilemur. 



The under side of the skull of Adapis parisiensis, as Dr. Stehlin notes (1912, p. 1202), differs from 

 that of modern Lemuridse in the large size of the bullae and in the size and strength of the pterygoid plate 

 of the alisphenoid. This character is somewhat less pronounced in Adapis (Leptadapis) magnus var. 

 leenhardti. Among the Lemuridse Mixocehus and Microcebus have large bullse, while Atililemur, Chiro- 

 gale and Myoxicebus have the bullse small and set well back near the occiput. 



The palate in all types of Adapis is produced behind m^ and ends in a median projection. In Lemur, 

 Lepilemur and Mixocebus the palate ends in front of m^. In Microcebus, Chirogale, Atililemur, however, 

 the palate is produced behind m^. In all the Lemuridse the median projection of the palatal border is 

 vestigial or wanting. The primitive notch Ijetween the vertical plate of the palatine and the alveolar 



' The phylogenetic interpretation of this character will be discussed by the writer in a later Bulletin of The American Museum of 

 Natural History. 



