GREGORY : 



NornARcrus, an American eocene primate 



169 



small ; while the small size of the dorsoposterior part of the periotic and the total exclusion of the mastoid 

 from all share in the cranial cavity, together with the relative narrowness of the base of the occiput, all 

 reflect the small size of the cerebellum as a whole. 



The olfactory fossa of the cranial cavity and its contained olfactory lobes were larger than those 

 of Propithecus coquerelli, but not quite as large as those of a large Lemur varius. In proportion to the 

 width of the frontal lobes, however, the olfactory lobes of Notharctus were much larger than those of 

 recent lemuroids, so that it may be classed as macrosmatic. There was a sharp constriction between 

 the olfactory and frontal lobes, corresponding to a high ridge on the endocranial surface of the frontals. 

 The width of both frontal and parietal lobes was considerably greater in the progressive N. oshorni than 

 in the conservative N. venticolus. 



As compared with the brain cast of Adapts figured by L. Neumayer ^ that of Notharctus is obviously 

 of the same general type, save that in Adapts the temporal lobes are more expanded transversely, and 

 project more prominently downward and forward behind the Sylvian fissure, both progressive characters 

 pointing in the direction of the modern Lemuroidea. The floccular process of the cerebellum, which was 

 lodged in the subarcuate fossa, in Adapis was larger than in Notharctus, another progressive feature. 

 This fossa is wrongly indicated by the number "8" in Neumayer's figures, as there is no reason to doubt 

 that the eighth nerve (marked "7") passed into the internal auditory meatus in the usual manner. The 

 surface of the cerebrum shows no sulci. 



THE COCHLEA AURIS AND OSSICFLA OF XOrilARCTUS; COMPARISON WITH OTHER PRIMATES 



Cochlea 

 Plate XLV 



Under the delicate manipulation of Mr. .Vnderson the type skull of Notharctus osborni (Amer. Mus. 

 No. 11466) has yielded not only a complete record of the anatomy of the interior of the bulla, but even 

 a section of the bony cochlea, together with the auditory ossicles of the right side. Mr. Anderson and 

 the writer have also made for comparison with Notharctus a series of preparations of the bony auditory 

 region of other primates, some of which are illustrated in Plates XLIII-XLVII. A second specimen of 

 N. osborni, Amer. Mus. No. 13030, includes the greater part of the periotic of both sides, showing the 

 internal auditory meatus, the subarcuate fossa, a section of the cochlea, and other details. 



As already noted, the general construction of the auditory region of Notharctus is identical with that 

 of Lemur and Propithecus, the chief difference being that in the Eocene genus the bullte are somewhat 

 smaller and less extended anterointernally. The course of the internal carotid canal and its stapedial 

 branch and the course of the Fallopian aqueduct also conform to the lemuriform type. Another import- 

 ant resemblance to the Lemuriformes is that the fenestra cochleae (f. rotunda) is concealed from a view 

 through the tympanic ring by the posttympanic process of the squamosal near its junction with the 

 carotid canal, whereas in Loris, Periodicticus, and Galago, representing the Lorisiformes, and in the 

 Platyrrhini, the f. rotunda is visible through the tympanic ring in the dried skull, after the removal of 

 the tympanic membrane, lying immediately below and somewhat behind the fenestra ovalis. 



Behind the fenestra cochleae and separated from it by the ventral surface of the cochlea lies the 

 posterior extension of the hypotympanic sinus, which is less expanded than in Lemur. The cochlea as 



' 1906, Ueber das Gehirn von Adapis parisieiisis Cuv., Neues Jahrb. f. Min. etc., II, pp. 100-104, PI. v. 



