316 N. W. INGALLS 



well known that there exists a relation between the thickness of 

 the gray lamina and the size of its foldings — cf. the cerebellar 

 cortex and the olive. But within these limitations his diagrams 

 show a considerable correspondence between areas and gyri. 

 Furthermore, with two hereditary factors at work, in the first 

 place the extent of the cortical area, with its individual variations, 

 and secondly its associated foldings, we can look for no more than 

 a general, though none the less essential, correspondence and this 

 can only be determined by the investigation of a large number of 

 cases. These considerations are amply sufficient to explain the 

 findings of Brodmann, whose descriptions are those of individual 

 and probably, though not necessarily, of average conditions. It 

 is very interesting in this connection to note that, in that area 

 which is most sharply marked off from others the relations of the 

 associated furrows are most typical and constant. We refer to 

 the area striata, the so-called visual cortex. 



We may take occasion here to mention the various kinds of sulci 

 which may arise in connection with the development of a given 

 ^rea and illustrate them on the area striata. They may be within 

 a given area or between adjacent areas or may sustain a sim- 

 ilar relation to more than one area. These inter- and intra-areal 

 furrows may be further grouped in the following manner (Elliot 

 Smith '07, p. 202) . Axial furrows ard formed by folding within an 

 area; the bounding furrows are either sulci limitantes or sulci 

 operculati depending upon the correspondence of the limits of the 

 area with the bottom of the sulcus or with one lip (operculum) 

 of the same. The sulcus retrocalcarinus or posterior calcarine is 

 an axial furrow, the sulcus calcarinus proprius, anterior calcarine 

 is a sulcus limitans, while the sulcus lunatus, and t5^pically also 

 the inferior occipital in lower forms are sulci operculati. 



Some general conclusions on the localization in primates may 

 be drawn from the works and certain brain-charts reproduced here 

 (figs. 12-17) of the above cited investigators. It is evident that the 

 increase in the complexity of fissure formation and in the number 

 of areas which can be distinguished has not been uniform. This 

 lack of uniformity is, of course, the very essence of specialization. 

 In other words, there has been relative increase or decrease in 



