No. i.] OSTEOLOGY OF PCEBROTHERIUM. 59 



one hand, the shape and position of the posterior nares, on the 

 other, in P. occidentalis ; in P. angustidens the extension of the 

 frontal zone and posterior position of the orbits, combined with 

 the very camel-like cranium. 



III. The Brain. 



The salient features of the brain of Pcebrotherium are the 

 large relative size of the cerebellum and medulla, the short, 

 narrow, and tapering hemispheres, which in the anterior region 

 have very slight vertical depth. The convolutions are few, 

 simple, and straight ; and the sulci present are, with the excep- 

 tion of a few accessory ones, those which are common to the 

 whole series of ungulates, and closely resemble those of a foetal 

 sheep. The frontal lobes are strikingly small. 



The brain of Procamelus, as described and figured by Cope, 

 shows a decided advance upon that of Pocbrotherium. The cere- 

 bellum is relatively smaller and the hemispheres larger, and they 

 have assumed a more rounded and less tapering shape : the 

 frontal lobes are decidedly enlarged, the accessory sulci have 

 become more numerous, and the convolutions somewhat more 

 sinuous, though they are still much simpler and straighter than 

 in the recent genera. This brain is "not materially smaller 

 than that of the llama, an animal which Procamelus equalled in 

 general proportions. The hemispheres are, however, not pro- 

 duced so far posteriorly as in the Auchenia, reaching only to 

 the line of the meatus auditorius externus. 



"The orbital portion of the hemispheres is extensive and 

 nearly smooth from the olfactory lobes to the supra-orbital 

 border. This is not prominent, but is represented by a short 

 longitudinal ridge. Above each of these, on the superior or 

 front aspect of the hemispheres, is a massive convolution, but 

 crescent-shaped, with the convexity inwards. The posterior part 

 of the convolution is a sub-round tuberosity, which stands oppo- 

 site to, and in front of, the furrow separating the Sylvian and 

 median convolutions" (No. 6, p. 339). 



The change from Procamelus to the recent species in brain 

 structure consists less in increase of size, though there is some 

 such increase, than in the rounder and deeper shape of the 

 hemispheres, and in the very much more numerous and more 



