416 . PEOF. 0. ELLIOT S:\iriH ON THE 



showed. Tlie Sylvian, " lateral," " coronal," postsylvian," and orbital are (|uite lemuvoid 

 in position and constitution. The presence of the small and variable sulcus ia front of 

 tiu" intraparietal j^lateral] sulcus completes tlie resemblance. 



The possibility of recogiiizinij,- a central sulcus in the Lemurs has recently been 

 discussed by Beddard *, wlio believes that " the lemui-s are to be differentiated from 

 the higher primates by the fact that their T)rains do not exhibit any trace of a fissure of 

 Rolando [central sulcus], so constant a feature of all monkeys and apes." To justify 

 the latter statement he regards the anterior extremity of the intraparietal [his " supra- 

 angular "] sulcus as the representative of the central sulcus, chiefly because it " is in an 

 ideal i^osition for a fissure of Rolando"; i.e. it is midway between the anterior and 

 jiosterior poles of the hemispheres, which according to Beddard is the position of the 

 central sulcus in the genera Ateles, llycetes, Cehus, Bmchijurus, and Lagothr'ix. This 

 argument, however, is quite fallacious because it ignores tlie fact that a relatively 

 enormous increase in the extent of the pallial area in front of the Sylvian fissure occurs 

 within the family Cebidic, so that in the lowlier members of the Family the central 

 sulcus, if present, must be placed relatively nuidi further forward in the hemisphere 

 than it is in the lar^rer "'enera. An indication (jf such a teudencv is exhibited in the 

 brain of I'UIiccid. 



In the earlier memoir of Ziehen a very different interpretation of the homologies of 

 these sulci is suggested ; and Beddard makes no attempt to refute these arguments. 

 Ziehen regards the sulcus wliicli is found in front of the lateral sulcus in Pcrodicficus 

 as tlie central; he also considers that in Ni/aticcbiis the central sulcus is represented by 

 the two sulci /'and .;■ + y. 'Ilie sulcus /'in the genus Lemur is considered by Ziehen to 

 represent the central sulcus or the upper portion of it, whereas Elatau and Jacobsohn t 

 anticipated Beddard in regarding it as " precentral." These writers then proceed to 

 criticise the argument of Ziehen that the furrow/ represents the central siilcus, because 

 it occupies the appropriate position in regard to the lateral (intraparietal) sulcus. They 

 argue that the sulcus in question might with equal justice be i-egarded as the sujierior 

 precentral by reason of its relationship to the coronal (their sulcus "' frontalis"), utterly 

 ignoring the fact that the precentral sulcus never occurs in the absence of the more 

 stable central sulcus. 



They further lu'ge, in opposition to Ziehen's suggestion, the T- or Y-shape of the 

 sulci, their sagittal direction, and the fact that, according to Chudzinski's diagram, there 

 is a sulcus resembling the supposed central sulcus of Lenin}- in front of a definite central 

 sulcus in the l)rain of Iiulris. They summarize their criticism of Ziehen's conclusions 

 regarding the central sulcus in these words : — " Die Moglichkeit, dass der untere der 

 beiden qtieren, hinter dem Sulcus frontalis [coronalis] gelegeneu Furchen [i. e. tlie 

 sulcus ^ of i<?»i«/- and the sulcus x f ^ of Xyct'tcehus] homolog dem Sulcus centralis 

 der Affen ist, lasst sich niit absoluter Sicherheit nicht bestreiten, wenn auch die Gestalt 

 uiul Lage der Furche luehr dem Sulcus pra-eentralis (arcuatus) ents])richt ; die obere 

 [sulcusy] der beiden queren Furcheu ist aber sicker ein Homolog des Sulcus pra?con- 



« •>'.jvitates' iUOK p. :3(j5. t •Haudbutli; p. ITS. 



