( 366 ) 



may consider that in this Platyrrhinc monkey the further development of the snpra- 

 angular fissure of the Lemur into iutra-parictal and fissure of Rolando is apparent. 

 I cannot, of course, jmt forward this view of the homoloj^ies of the iissnres in questi<in 

 as more than a theory, not, I trust, nnsujijiorted hy fact. This interpretation is 

 apparently in liarmouy with the results obtained by Kiikenthal and Ziehen from an 

 e.xamination of the brain of C iii(jrifro».s. As far as 1 can see from their fiy:nre 

 a small fissure lettered n and homologised with the centrnU.s (i.e. fissure of liohuulo) 

 is the cut-off end of the continuous supra-angular fissure of ( '. torqmitu. It is at 

 least reasonable to seek for the nearest approach to the underlying Lemurs in the 

 Platyrrhines rather than in the Catarrhines. As to the small transverse fissure 

 behind, which may be regarded as forming a boundary line between the ])arietal and 

 occipital regions of the brain, I am disjiosed to consider it to be the Simian fissure 

 (" Affenspalte " of the Germans), since the parieto-occipital seems to be represented 

 by the tiny indentation in the middle line of the hemispheres produced by the 

 meso-occi]iito-])arietal, where it just reaches the surface. This matter, however, 

 I do not venture to elaborate further. 



Some of the fissures on the internal surface of the cerebral hemispheres are 

 rather different from the corresponding fissures of CalUthrix gigot and C. nigrifrons. 

 In the first place, there is a strongly marked meso-jiarieto-occipital, which, instead 

 of being oblicjue in its directions, runs downwards at right angles to the longitudinal 

 axis of the brain. This seems to be absent or feebly devek)i)ed in both C. nigrifrnns 

 and C. gigot. In C. tonjuata it very nearly joins the calcarine. The latter fissure 

 is also well developed, and the collateral fissure is difl'erent from that of C. gigot. 

 In the latter the fissure runs obliquely upwards, and is branched anteriorly. In 

 C. torqtutta the fissure passes directly upwards and then runs jjarallel for a little 

 distance to the calcarine. The calloso-margiual is not very well marked in 

 C. torquata. 



We can abstract from the observations now made upon the brain of this 

 genus the distinguishing features which contrast with other New AVorld monkeys. 

 In CalUthrix there is an intra-parietal fissure, joining anteriorly a rudiment of the 

 fissnre of Rolando, and ending posteriorly in or close to a Simian fissure. The 

 Sylvian and antero-temjidral fissures do not join above. The occipital lobe, save 

 for the last-mentioned fissure, is smooth. The frontal lobes are furrowed by a 

 rudimentary pro-Rolandic and supero-frontal fissures. The meso-parieto-occipital 

 fissure (when present) is at right angles to the long a.xis of the brain, and nearly 

 joins the calcarine. The collateral fissure is sometimes also vertical in direction. 



It is clear, from what is now known about the brain of this monkey, that it is 

 one of the simplest of those of the Platyrrhine monkeys. This fact is, of course, 

 clearly in accord with their small size, the larger Atclcs and Lagothri.c having more 

 comjilicated liraius. 



