^UC 22 1903 [ 319 ] 



X. On the 3forpholor/f/ of (hr Brain in the Mammalia, icith Special Reference to thai 

 of the Lemurs, Recent and Extinct. Bij G. Elliot Smith, M.D. {Sydney), Fellow 

 of St. John's CoUerfC, Cambridge, and Professor of Anatomy, Egypfiait Cocernment 

 School of 3Iedicine, Cairo. [Communicated by Prof. G. 13. Howes, D.Sc, LL.I) , 

 F.R.S., Sec. Linn. Sac.) 



(With C6 Illastrations in the Text.) 



Itead ULh Mareli, VJ(r2. 



Introductiox. 



1 HIS investigation was undertaken pi-imarily to consider the possihility of homologizing 

 the sulci of the cerehral hcmis2)herc in different Orders of Mammals. A^'itli thi.s ol)jcct 

 in view, the brain was examined in almost every genus in the whole class of Mammalia ; 

 but as this yielded such an immense and unwieldy mass of data, it became necessary, 

 both for the sake of clearness and conciseness of exposition as well as to admit of the 

 adequate discussion of the signiticance of the facts, to limit the sco])e of the enquiry, or, 

 rather, to select the most instructive body of evidence which might tyjiify the 

 conclusions to be drawn from a study of the whole mass of data. 



This process of curtailment has been accomplished in two ways. In the first place, 

 attention has been almost wholly concentrated on the consideration of the homologies of 

 tlic furrows called " calcarine " and " Sylvian." Tiiese are the only sulci (in addition, of 

 course, to the hippocampal and rhiual fissures) which are absolutely constant in all 

 Primates. At the outset of this investigation it became abundantly evident, firstly, 

 that if the calcarine sulcus is a distinctive feature of the Primates and is not represented 

 in the brain of other Mammalia, the search for homologues of the other, less stable, 

 furrow on the mesial surface of the hemisphere must a fortiori be utterly futile; and, 

 secondly, if the Sylvian flssiu-e of the Apes and Man is represented in other mammals by 

 no sulcus other than that inconstant and exceedingly unstal)le series of different * 

 furrows, which in various Carnivores, Ungulates, Edentates, Rodents, and Marsupials is 

 commonly called "Sylvian," the possibility of homologizing any sulcus on the lateral 

 aspect of the hemisphere of the Primates with a furrow on the surface of the brain ot 

 other mammals becomes utterly destroyed. That this not altogether obvious conclusion 

 must inevitably be drawn from the premiss just stated will be abundantly shown in the 

 following pages. "We shall, therefore, best arrive at some decision regarding the main 

 question, by devoting our attention chiefly to the Sylvian and calcarine furrows, without, 

 however, altogether neglecting the other sulci. In the second place, I have deemed it 

 desirable to further limit the dimensions of this work, by restricting the detailed account 



* Xon-homologous. 

 SECOND SERIES. — ZOOLOGY, VOL. VIII. 48 



