GREGORY : 



.\Y)TI{ARrTrS, AN AMERICAN EOCENE PRIMATE 



159 



and N. crassus the glenoid region permitted all the motions of the mandibular condyle which ha^'e been 

 described above (p. 148). The back part of the glenoid fossa and the postglenoid process articulated 

 with the downwardly produced posterior extension of the condyle; the smooth side of the entoglenoid 

 process articulated with the internal convexity of the condyle, while the deepest concave portion of the 

 glenoid fossa articulated with the convex summit of the condyle. The anteroposterior extension of the 

 glenoid fossa and glenoid ridge permitted a marked anterior displacement of the mandible. In Adapts 

 the flattened glenoid region permitted some anterior displacement but was apparently not so favorable 

 for the tilting and transverse movements of the mandible. 



The zygomatic process of the squamosal in A^. osborni was evidently slender; in iV. crassus, although 

 massive, it was surpassed by that of Adapis. The dorsal root of the zygomatic process is continued 

 above the external auditory meatus as a strong crest which bounds the area of the temporal muscle ex- 

 ternally and is continued upward into the lambdoidal crest, as in Adapis. In A^. crassus the lower ridge 

 of the zygomatic process is roughened for the attachment of the masseter. Apparently the posterior 

 extension of the malar did not extend back to the glenoid region of the zygoma as it does in Adapis but 

 was limited to the middle of the zygoma. On the posterior slope of the postglenoid process is the promi- 

 nent postglenoid foramen as in Adapis. The external auditory meatus is bordered above by a rim of 

 the squamosal, which forms an obliquely warped arch opening outward and backward. In A", osborni 

 this passage is wider than in A^. crassus. It is fundamentally similar to that of Adapis. The post- 

 tympanic process is small and fused with the anterior part of the mastoid region. 



Occiput 

 Text Fig. o(j 



The occiput is almost perfectly preserved in the type of A^. osborni and partly preserved in A^. crassus 

 (Amer. Mus. No. 12567). Its general aspect is similar to that of Adapis parisiensis (Stehlin, 1912, p. 

 1199), but in the female skull of A^. osborni the occiput is not so wide, the superior extension of the mastoid 

 is narrow, the foramen magnum is deeper and the articular facets of the condyles are flatter, more vertical 

 and more extended dorsally. In the male skull (A^. crassus) the lambdoidal and sagittal crests are much 

 higher, the general outUne of the occiput being almost triangular, suggesting rather the occiput of a 

 carnivore, except for its greater width at the base. The median superior tip of the occiput (inion) is 

 produced somewhat backward and ends in a tubercle for the ligamentum nucha^ not dissimilar to that 

 of Adapis; beneath this a sharp median crest separates the neck muscles of the right and left side. The 

 lateral extension of the exoccipital was apparently separated from the wide supraoccipital by the hori- 

 zontal fissure mentioned below (p. 160). The interparietal and supraoccipital are coalesced, so that their 

 limits could not be determined, but it is not likely that they extended forward on top of the skull as they 

 do in lemurs. 



The back of the occiput and of the lambdoidal crests served for the attachment of muscles which 

 were probably arranged essentially as they are in modern lemurs ^ and indrisines.'' Attached immedi- 

 ately beneath the rim of the lambdoidal crests was a series of la\^ers of muscles, the outermost two layers, 

 namely, trapezius, rhomboideus, being connected with the fore limb ; the next layer included the com- 

 plexus series (dorsal) and the splenius (lateral), representing the anterior continuation of the spinal series. 



' Cuvier and Laurillard, Planches dc Myologie. 



- Grandidier and Milne Edwards, 1870, Pis. xxxvr and xxxvii. 



