340 PKOF. G. ELLIOT SMITH OX THE 



If a vertical line he drawn from the most prominent part of the " natifoi'm 

 eminence" of the pyriform lobe, it Avill he found that more than half of the hemisphere 

 lies behind the vertical line. This is not the case in Lemui-, but is so in all Apes. 



There is a more pronounced caudal extension of the hemisphere, so that the cerebellum 

 is almost completely overlapped. 



There is a much smaller " orbital area " in Nycticehus than in Lemur. In the latter 

 it extends in the caudal direction as far as the pseudosylviau sulcus, whereas in the 

 former it only extends to a point midway between the pseudo.sylviau sulcus and the 

 anterior jwle of the hemisphere. 



In the genus Lemur the olfactory bulb is a horizontally flattened jdate, the bulk of 

 which is covered by the hemisphere. In the genus Ni/clicebiis the bulb is a vertical 

 sagittal plate, 5 mm. of the length (9 mm.) of which projects beyond the anterior pole 

 of the hemisphere. It is only 1-5 mm. broad (/. e. transverse thickness). 



The anterior rhinal fi.ssure is not obliterated : of the posterior rhinal fissure only one 

 or two millia:ietres exist as a furrow, but if a i'resh brain be examined a very faint 

 depression is visible extending horizontally backward Avith a slight downward Ijend. 

 This can be traced on to the mesial surface. 



The flexure of the ])yriform lobe is slightly more acute and pitliecoid than that (jf 

 Lemur, so that the vallecula Sylvii is more cleftdike. Tiie other parts of the rhiuen- 

 cephaloa closely resemble the corresponding regions in the genus Lemur, with the 

 exception of the lower end of the hipj)0campus. Eor in Nycticebus, iinlike every otliei- 

 Prosimian known to me, there is no well-defined hippocamiml tubercle. The inverted 

 hippocampus merely becomes slightly broader at its lower end, as it does in most 

 mammals (fig. 12). 



6 re. 



I. 

 fh. 



Kyeiicehus tardigradns. 

 Mesial aspect of the right cerebral hemisj/here. Kat. size. 



The corpus callosum is a very thin plate of fibres 12 mm. long; its anterior and 

 posterior parts are not so markedly thickened as they are in Lemur. There is an 

 exceptionally extensive arcuate genu. 



The form and relations of the calcarine group of sulci are identical with those 

 described in Lemur. The paracalcarine sulcus is, however, much shorter. The 

 intercalary sulcus is relatively larger than it is in Lemur, and its posterior extremity 

 is slightly bifid : the upper limb being the deeper faintly foreshadows the upturned 

 posterior end of the calloso-margiiial sulcus of the Anthropoidea. There is neither 

 a genual nor a rostral sulcus. 



