GREGORY: NOTHARCrVS, AN AMERICAN EOCENE PRIMATE 



161 



but, as shown in Amer. Mus. No. 12569, it lies at the bottom of a deep fissure which is closed at the top, 

 as if the vein transmitted by the foramen had sunk deeply into the mastoid after passing above it in the 

 embryo. Stehlin does not describe the mastoid foramen in Adapis. The mastoid has a deep fossa on 

 its ventral surface as in Adapis. Possibly this fossa may have given attachment to the digastric. The 

 S-shaped groove described by Stehlin in Adapis (1912, p. 1201) on the lower surface of the mastoid was 

 not recognized in Nothardus. The interior of the mastoid (Amer. Mus. No. 12569) was pneumatic. The 

 stylomastoid foramen opens on the ventral surface of the mastoid behind the carotid foramen (see p. 178 

 below) ; it leads into a bony canal which traverses the periotic anteroposteriorly and receives the stapedial 

 canal (see p. 178 below) and which is therefore the Aqueduct of Fallopius. (Plate XLIV; Figs. 58-62.) 



Occipital Condyles 

 Text Figs. 56, 5S, 02 



The posterior face of the condyles is flattened and vertically extended, while the ventral surfaces 

 are more extended transversely and less produced anteroposteriorly than in Adapis. The median part 

 of the basioccipital between the condyles shows a faint articular facet for the ventral rim of the axis in 

 flexion of the head; while the deeply concave intercondylic rim is facetted for the stout odontoid process. 

 The general form of the condyles indicates that the atlas had a relatively deep and narrow cotylar facet, 

 that motion of the skull upon the atlas was more nearly transverse and less oblique than in Adapis and 

 probably that the inclination of the skull to the atlas-axis complex was less than in that genus. 



Basioccipital 

 Text Figs. 58, 02 



As the whole skull is longer and less widened than that of Adapis the same is true also of the basi- 

 occipital. The basioccipital-basisphenoid suture ends anteriorly on a line with the anterior extension 

 of the bullae, while in Adapis this suture is considerably behind the front ends of the bulla? (Stehlin, 1912, 

 pp. 1168, 1255, figs. 244, 280). The median ridge of the basioccipital is quite pronounced, as well as the 

 fossae on either side of it, which gave insertion to the stout recti capitis antici (major and minor) muscles. 

 The lateral border of the basioccipital is raised into recurved alse overlapping the medial base of the bullae 

 after the fashion of the tympanic processes of the basioccipital of Insectivores. In Adapis, on the other 

 hand, these flanges are absent (Stehlin, 1912, pp. 1254, 1255, figs. 279, 280) or but faintly indicated 

 (idem, p. 1168, fig. 244). The condylar foramen is continued forward into the foramen lacerum posterius 

 as it is in Adapis magnus var. leenhardti (Stehlin, 1912, p. 1279, fig. 287), but the jugular foramen is 

 distinct. In A. parisiensis var. hrwii (Stehlin, p. 1201, fig. 259) the foramen lacerum posterius is well 

 separated from the condylar foramen. The encephalic surface of the basioccipital is not known. 



Auditory Region 

 Plate XLIV; Text Figs. 58, 02 

 This region is remarkably well preserved in the type of A^. osborni, and, thanks to the skill of Mr. 

 A. E. Anderson, it reveals for the first time the intricate anatomy of the internal ear and auditory ossicles 

 of an Eocene mammal. The cochlea auris and ossicula of Adapis not being known for comparison, the 

 description of these parts in Nothardus will be given in another section of this paper (pp. 160, 170 below) ; 

 but the region of the tympanic cavity may be compared with that of Adapis, which has been fully described 



