206 



THE LOWER PRIMATES 



frontomarginalis. The parietal lobe is well demarcated, its caudal iaoundary 

 being established by the inception of the sulcus simiarum. The occipital lobe 

 as a whole shows considerably more expansion than in the case of lemur or 



FIG. 113. LEIT LATERAL SURFACE OF BRAIN, MYCETES SENICULUS. 



(Actual Length, 52 mm.] 



Key to Diagram, obl.. Oblongata; ram. post., Ramus Posterior of Superior Temporal Sulcus; sulc. 



PRECT. INF., Sulcus Precentralis Inferior; sulc. ret. inf.. Sulcus Retrocentralis Inferior. 



marmoset. The temporal lobe, perhaps more than any other portion of the 

 lateral surface, shows a tendency toward that progressive advance which 

 eventuates in the fully developed characters of this region in the primate 

 brain. 



THE BASAL SURFACE OF THE HEMISPHERE AND THE OCCIPITAL CONCAVITY 



On the basal surface of the hemisphere, the two orbital concavities are 

 well defined, as are also the interorbital keels. The olfactory bulb and tract 

 show a considerable decline in prominence and are detachable as far back 

 as the trigonum olfaetorium. The lateral root of the olfactory tract is much 

 less prominent than in either the marmoset or the lemur, indicating in a 

 general way the tendency toward deflorescence in the development of the 

 olfactory central mechanism. 



The occipital concavity is pronounced in mycetcs due both to the expan- 

 sion of the lateral lobes of the cerebellum and the further expansion of the 



