MOHPIIOLOGV OF THE BRAIN TX THE ^FAMMAMA. H?.'' 



Sylvian tissuve in othei- brains, it will be seen that tiic position of tliis " Sylvian ttssiire" 

 ill Tarsliis is very peculiar. The further discussion of the sipjniflcance of this furrow 

 w ill be more intelliij:ible if it bo postponed until the nature of the Sylvian lissiire of tlie 

 other Lemurs has been considered. 



Apart from tiiis sulcus, the rest of tli(> cranial as|);»ct of tiu^ hemisphere is smooth ami 

 devoid of sulci. 



There is a very slii^-ht llattenini;', unworthy of the u;un(> of furrow, just behind and 

 parallel to the caudal margia of the orbital excavation. It may possibly represent the 

 postsylvian sulcus. 



,\n even slig'liter flattening is found parallel to the mesial plane in a situation wliei-e 

 the intraparietal (lateral) sulcus is found in other Lemurs. 



\n view of the considerable dillerences whicii are shown to exist by comparing the 

 brains of various Lemurs, the resemblance between the brains of Tars/us and the smaller 

 Galaginie is a fact of considerable significance. The peculiar features of the calcarine 

 group of sulci so strikingly re2:)roduce those found in all the other Prosimiie, and in no 

 other mammals of a similar size (with the possible exception of the Edentate Mani-s), 

 that they alone constitute an important indication of the closeness of the bond of affinity 

 Avliich unites Tavsiits to all the other Lemurs. 



It is also jieculiarly instructive to note that the chief diff'erences between the brain of 

 Tarsiits and the other Lemurs occur in the commissural region ; and in respect to this 

 Tarsins approximates much more nearly to the primitive nrammalian type than do the 

 other Prosimite. 



As in Microcebus, Tarslus possesses only one sulcus other than the calcarine grou)) 

 (and, of course, the hippocampal fissure). This other sulcus is the Sylvian or, perhaps, 

 its suprasylvian element. In these respects these small Frosimian brains resemble those 

 of the lowlier Apes. 



In Galago small lateral and orbital sulci make their appearance on the outer aspect, 

 and intercalary and rostral sulci on the mesial surface. In the Great Galago the lateral 

 sulcus becomes longer, and a coronal sulcus makes its appearance ; the sulcus/ and th(; 

 postsylvian furrows also may become developed. 



In tlu' larger Lemurs diagonal postlateral, collateral, and other furrows may develop. 



TlU: BUAIN-SIKM. 



By this term I mean those parts of the brain which remain after removing the 

 cerebral hemispheres and cerebellum. 



In my Memoir on the Brain in the Edentata I pointed out that these parts are subject 

 to much less variation in the ditfereut mammalian Orders than are the cerebral hemi- 

 spheres and cerebellum. A careful study of these regions in T<u->iius, Lemur, Microcebius, 

 and, by macroscopic means only, in Chiromys, Galago, and several other Prosimiie, has 

 revealed no features which are not equally peculiar to all mammals, so tliat no lengthy 

 consideration of these regions is necessary. 



There is practically nothing concerning these parts of the brain in the literature of 



