v] ritttio-SciiMH-i/ Area In the Anthropoid A IK' \'1\ 



what has been said already concerning the influence which the position of the calcarine 

 fissure exorcises over the distribution of the area. 



In his jiajier on the exact histological localisation of the visual area, Bolton mentions 

 the presence of two polar sulci, which he describes in the following words, "small, more or 

 less semilunar fissures, which are invariably found surrounding the posterior extremities of the 

 calcarine fissure and which are frequently distinct from the anterior and lateral occipital 

 fissures," and he states further that these fissures form constant boundary lines for the visual 

 area. Since the publication of Bolton's work I have repeatedly defined these fissurets, also 

 I am able to endorse his statement that they form constant limits for the visual area, 

 that is, provided the field over which a calcarine type of cortex is distributed be considered 

 synonymous with that area. 



But with the exception of these fissurets, there is certainly no sulcus on the postero-lateral 

 surface of the human brain which seems to exert a constant influence on the disposition of 

 the area; its relation to the lateral occipital sulcus of Eberstaller is as uncertain as the 

 distribution of that sulcus is variable, a wide zone separates it from the transverse occipital 

 sulcus of Ecker, and as the " external " calcarine fissure, which according to Cunningham 

 is present in the foetal brain, defies definition in at any rate the majority of adult brains, 

 it cannot be said to be related to it. (See also footnote p. 125.) 



DISTRIBUTION OF THE CALCARINE TYPE OF CORTEX IN THE ANTHROPOID APE. 



(Text-figure 11.) 



From the phylogenetic standpoint it is important to compare the distribution of this 

 type of cortex in the higher apes with that in man, and on doing so it is interesting to 

 find that in the brains of both the same type of structure clings closely to the calcarine 

 fissure, and that, in consequence, a view of the mesial surface of the hemispheres shows 

 a marked resemblance between the respective areas. It is more interesting to discover that 

 on the postero-lateral surface there is a vast difference, the anthropoid area being infinitely more 

 extensive than the human; while a further and a still more important distinction, to which 

 I shall have to allude in detail presently, is that in the higher ape the distribution of the area 

 is definitely influenced by and related to certain sulci on the external surface of the occipital 

 lobe, sulci which in themselves as anatomical units constitute distinguishing features between 

 the two brains; I refer to the "external calcarine fissure" and the " Affenspalte." 



Since the distribution of the area which I have mapped out in the brains of the chim- 

 panzees submitted to examination does not differ materially from that which I have defined 

 in the orang, separate descriptions are unnecessary, and the following lines will embody an 

 account of the delimitation of the area in both animals. 



Starting with the anterior part of the area, again we find that the special type of structure 

 does ii"i roach quite to the anterior extremity of the "stem" of the calcarine fissure, and 

 that it first makes its appearance on the lower or lingual wall of the sulcus ; so far resembling 

 the human arrangement; but it very rapidly crosses the floor and climbs the upper wall, 

 and in this respect the anthropoid and human brains differ; for it will be remembered that 

 in the latter the calcarine type of cortex, as a rule, is confined entirely to the inferior wall 

 and lip of the "stem" of the fissure. 



An explanation of this deviation in the delimitation of the calcarine cortex in the anthropoid 

 brain is not far to seek, for in all three specimens which I have examined the annectant 



c. 16 



