1903.] the Betrocalcarine Region of the Cor tec Cerebri. 



61 



represents the anterior boundary line of the stria-bearing cortex, the 

 sulcus retrocalcarinus lies wholly within that area (fig. 1). 



If a section be made through any part of the true calcarine sulcus 

 (except its extremities), the ventro-cauclal lip of the furrow will be 

 found to contain the stripe of Gennari, which stops sharply opposite 

 the bottom of the sulcus and does not invade its dorso-cephalic lip 

 (fig. 1, A). I have demonstrated this relationship in a large series of 

 Egyptian and Soudanese brains. It is clear that the true calcarine 

 sulcus accurately marks the line of separation of the area striata and 

 the gyrus fornicatus. In a previous work* I was led to the conclusion 

 that the calcarine sulcus on the mesial surface and the suprasylvian 

 sulcus on the lateral surface of the cerebral hemisphere are probably 

 due to some causes other than the mere general expansion of the 

 neopallium, because they occur with such remarkable constancy in 

 the most diversely-specialised Mammalian Orders, in which the 

 mechanical conditions moulding the growing cortex must be far 

 from uniform. In the case of the suprasylvian sulcus I stated 

 reasons for believing (p. 410) that these other causes were to be 

 found in the unequal rates of growth of the receptive area for 

 auditory impressions and a more dorsal region performing some other 

 function. 



The true calcarine sulcus is also probably the result of the dis- 

 proportionate expansion of two neighbouring areas of different 

 physiological significance. 



If we admit the validity of the teaching of Henschen, Vialet and 

 others, f who regard the visual centre as being exactly limited to the region 

 distinguished by the stripe of Gennari, we can conclude that the true 

 calcarine sulcus is caused by the unequal rates of growth of the visual 

 area and the cortex in front of it, which performs some other function. 



If the brain of any large Carnivore or Ungulate be examined (in 

 sections either of the fresh brain or after staining according to Weigert's 

 method), the area striata will be found to be limited anteriorly on the 

 mesial surface of the hemisphere by the retrosplenial part of Krueg's 

 " splenial sulcus." The stria extends into the caudal lip of the sulcus 

 and ceases abruptly opposite the bottom of the furrow. This affords a 

 striking confirmation of the view, which I put forward last year:}: on 

 general morphological grounds, that the retrosplenial part of Krueg's 

 splenial sulcus in the Ungulata, Carnivora, and other Mammalia is the 

 strict homologue of the carcarine sulcus (in the restricted sense just 

 explained) of the Human brain.§ 



* Op. cit., supra, 'Linn. Soc. Trans.,' 1903. 



f See S. E. Henschen, "Eevue Critique de la Doctrine sur le Centre Cortical do 

 la Vision," XHIe Congres International de Medicine, p. 130, Paris, 1900, trans- 

 lated by Dr. Dor. 



X Op. cit., supra. 



§ Op. cit., 'Linn. Soc. Trans.,' 1903, p. 376 et seq. 



