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291 
posterior surface is much smaller, though very distinct, and increases with 
advancing age to the fully adult condition. The position of the external 
auditory meatus is much the same as in Nesodon, but the mastoid is ex- 
cluded from the surface of the skull and the postglenoid and post-tym- 
panic processes of the squamosal are fused together. 
Even if Roth’s identification of the mastoid in the Toxodonta should 
prove to be correct, it would not indicate any radical difference from the 
Fig. 45. 
Sus scrofa. Occiput, X S.oc., supraoccipital ; 
Exoc., exoccipital; P.oc., paroccipital ; M.a.e., exter- 
nal auditory meatus; Sq., post-tympanic portion of 
squamosal; Zy., zygomatic process. 
Fig. 46. 
Procavia capensis. Occiput, X f. S.oc., supra- 
occipital; Exoc., exoccipital; P.oc., paroccipital 
process; P.g., post-glenoid process; Mas., mastoid 
portion of periotic. 
Hyracoidea (see Text-fig. 46) in which the posterior surface of the skull is 
completed by the large, inflated mastoids, the cavities of which are filled 
with cancelli. The mastoids are ankylosed with the tympanies, but 
usually not with the squamosals, though in some species the latter fusion 
also occurs. 
Roth’s view of a near relationship between the “ Notoungulata” and 
the Primates, and radical distinction from all other hoofed animals, involves 
such a degree of convergence as staggers belief. It further involves, as 
