:\FORPlIOLOGr OF THE J5RAIX IX THE [MAMMALIA. :V.)o 



TuK Morphology of the Sulci ox tiik Lateral and Dorsal 



ASPECTS of the CeREBRAL HEiriSPIIEKK. 



Iiinninerablo attempts liave been made, with results as vari(!d as they are numerous, 

 to solve the problem of determining to how great an extent, if at all, it is possible to 

 institute exact comparisons between the sulci of two brains. 



If the two hemispheres of any highly convohitcd brain I)e cr)mpai-ed, a certain number 

 of furrows Avill be found in eacli, wliieh cannot l)e exactly liomolos-ized witii any sulcus 

 in the other hemisphere. And not unnaturally the number of such "incomparable" 

 elements increases when we compare the hemispheres of different individuals, species, 

 genera, families, and orders. The crucial question is thus reduced to the enquiry as to 

 the possibility of recognizing any sulci as the common property of several Oi'ders. 



The most divergent and mutually contradictory views are held at the present time on 

 this subject. Thus there is the negative teaching, which is perhaps most forcibly and 

 dogmatically expressed in a posthumous memoir by A. J. Parker in these words: — 

 " Tiie mistake is ol'ten made .... of attempting to compare their [the Mammalia in 

 general] convolutional characters with those oi' the Primates, including Man .... We 

 cannot expect, nor do we find, any exact honiological relations between the convolutions 

 of this phyllum [sic] and those of other mammalian phylla [sic] " *. The same view is 

 expressed in a less jn'onounced form by D. J. Cunningham. 



The view of Gegenbaiir may be summed up in his own words by the statement " dass 

 eine Homologie nur in sehr engen (Jreuzen besteht und bei sehr vieleu gar nicht durch- 

 fiihrbar ist " (Vergl. Anat. der Wirbelthiere, i. Band, 1898, p. 769). 



Although in many of his earlier memoirs Turner had instituted comparisons between 

 the sulci in different mammalian Orders, yet in his kitest contribution he comes to the 

 conclusion that in each Order of Mammals a special pattern of sulci is evolved peculiar 

 to itself. 



Most other writers who have in any way dealt with this subject have come to the 

 conclusion that it is possible to homologize the sulci of Primates to a greater or less 

 extent with those of other mammalian Orders, luit there is an infinite variety ol' 

 siiggestions as to tlie exact manner in which this is to be done. 



Before avc consider a few of the suggested interpretations, it will conduce to clearness 

 if I first explain, by a reference to the Cat's brain, the nomsnclature employed in 

 describing the sulci in Orders other than the Primates. 



The furrow commonly called " Sylvian fissure " is an offshoot of the rhinal fissure : 

 as the usual designation is undoubtedly erroneous, I shall call it the pseudosylvian sulcus 

 (fig. 56 i). The sulcus which is best known by the name "presylvian" {Owen), I have 

 termed "orbital" for reasons which will be apparent later. The furrow which is 

 commonly called " posterior suprasylvian " has been designated by its original name 

 " postsylvian " {Owen), not only because the latter is more appropriate, but chiefly that 



* " llorpholog)' of the Cerebral Convolutions with Special Kei'erence to the Order of Primates," Journal ot the 

 Acad, of Xatural Science, Pliiladelphia, 2nd series, vol. x. 18!Mj, p. 27(). 



