210 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



pouch of the maxillary is present in Adapts but has been converted into a tunnel in all the Lemuridse. 



Notwithstanding the sharp divergence of the internal and external pterygoid plates in Adapts, 

 implying a strong development of the internal pterygoid muscle, the pterygoid bone itself is but weakly 

 developed and lacks a hamular process, which is present in the Lemuridse. 



The occipital condyles of Adapts are wider than those of Lemur and directed more posteriorly. In 

 Chirogale, however, the condyles are more like those of Adapts. 



The interior of the brain-case of Adapts offers a few marked differences from Lemur: the roof-shaped 

 projection of the presphenoid ( ?orbitosphenoid) above the optic foramina is wanting in Lemur; and so is 

 the crest (crista petrosa) upon the dorsal ridge of the petrosal, to which is attached in Lemur the ten- 

 torium. The posterosuperior process of the alisphenoid, which in Lemur arches over the foramen ovale 

 and overlaps the encephalic surface of the petrosal, is wanting in Adapts. The postglenoid foramen 

 is not visible from the cerebral surface in Adapts as it is in Lemur and there is some difference in the 

 course of one of the veins that drain through this foramen (Stehlin, 1912, p. 1218). In Adapts the roof 

 of the sinus hypotympanicus takes a greater part in the cerebral cavity. 



Mingled with these differences, there is perhaps an equal number of resemblances in skull structure 

 between Adapts and Lemur, as observed by Stehlin. Many of these, however, are also preserved in the 

 Indrisidse and therefore for the most part belong to the heritage of the Lemuriformes. These agree- 

 ments, which are in addition to those formerly discussed, may be summarized as follows. 



(1) Preorbital region of the maxilla bearing a shallow^ fossa for the prseorbicularis dorsalis muscle. 



(2) Nasals narrow essentially as in Lemur. 



(3) Infraorbital canal often double (it is frequently double in L. mongoz). 



(4) Internal nares wide and low. 



(5) Bullae with two anterior processes: 



(a) processus anteromedialis, articulating with basioccipital and basisphenoid. 

 {h) processus styliformis, connecting with external pterygoid plate. 

 (G) A horizontal ridge separating the temporal fossa from the external pterygoid fossa, running 

 from the glenoid to the orbitosphenoid. 



(7) External pterygoid plate pierced by foramen Civininii (pterygospinosum). 



(8) With minor differences, osseous elements and pattern of brain-cavity substantially as in Lemur: 



(a) orbitosphenoid sharing but little in the brain-cavity; 

 (6) squamosal also sharing but little in the brain-cavity; 



(c) petrous roof of sinus hypotympanicus taking a large share in brain-cavity; 



(d) topography of encephalic side of petrosal essentially the same as in Lemur: a capacious- 



fossa subarcuata above the internal auditory meatus ^ ; mastoid excluded by petrosal from 

 brain cavity; 



(e) foramina in back of orbit essentially as in Lemur (optic, for. lac. ant., for. rot., for. cranio- 



orbitale) ; 



(/) venous sulcus occipitalis .superior as in Lemur; 



(g) a considerable portion of the cerebral venous blood draining through the foramen magnum 

 and venffi vertebrales (Stehlin) ; 



' Examination of this region in representatives of all the major groups of Primates shows that the orifice of the subarcuate fossa 

 is always surrounded by the superior semicircular canal. This was also verified in a specimen of Nothardus osborni (Amer. Mus_ 

 No. 12569.) Presumably the rule will hold good also in the Adapinae. 



