118 Visuo-Sensory and Visuo-Psychic Areas [CHAP. 



DISTRIBUTION OF THE CALCARINE TYPE OF CORTEX. (Text figure 11.) 



As this type of cortex has such important relations with the calcarine fissure it is 

 necessary before discussing its limits that we should have a clear understanding concerning 

 some points in the anatomy of this fissure. A close examination of several hundreds of 

 brains and casts which I have prepared for the museum at Rainhill Asylum convinces me 

 that there is no reason for departing from the description of the fissure given by Professor 

 Cunningham in the Memoirs which he published in 1892, and the following remarks have 

 been abstracted from his work. 



He divides the fissure into two portions, an anterior part, or stem, which he would call the fissura 

 calcarina anterior and a posterior part, or fissura calcarina posterior. The fissura calcarina anterior, or stem, 

 is that part of the fissure which lies anterior to the junction with the parieto-occipital fissure, and it differs 

 from the posterior portion in being much deeper and in being a "complete" fissure. 



The stem is separated from the parieto-occipital fissure by the deep annectant gyms (the gyrus cunei 

 of Ecker or inferior internal pli de passage of Gratiolet). 



A deep annectant gyrus is likewise interposed between the stem and the posterior portion of the calcarine 

 fissure. This barrier may generally be found at a short distance behind the apex of the cuneus, and as it 

 connects the cuneus and lingual lobule it has been named the anterior deep cuneo-lingual gyrus. 



The posterior calcarine fissure in addition to being shallower is also somewhat shorter than the anterior, 

 its average length being 35 mm. against 40 mm. ; furthermore, it is divided into two parts posteriorly, by 

 a deep annectant gyrus which traverses its floor and connects the cuneus with the posterior part of the 

 gyrus lingualis. This is called the posterior deep cuneo-lingual gyrus. 



It is common to find this annectant reaching the surface (according to Cunningham, in 20/ of cases) 

 and completely cutting off the posterior forked extremity of the fissure, a vertically placed subdivision which 

 also goes by the name of the fissura extrema of Seitz or retrocalcarine fissure of Monakow. 



In regard to the position of this vertical offshoot it is to be noticed that although it lies close upon 

 the margin of the hemisphere it usually remains confined to the mesial surface, in other words it does not 

 extend to the convexity of the hemisphere 1 . 



Now concerning the distribution of the field of cortex bearing a line of Gennari, 

 reference to fig. 11 will show how its position is influenced directly by the calcarine 

 fissure and how it follows closely every bend and branch of this sulcus. 



In describing its distribution in detail it will be convenient to refer to the appearances 

 presented by a series of sections made at right angles to the calcarine fissure. In such 

 sections it is found that the arrangement does not reach quite to the anterior extremity 

 of the stem or anterior calcarine fissure but commences at a point from 5 to 10 mm. 

 further back. It first shows itself on the lower wall of the sulcus about half way down, 

 and as we proceed backwards, it gradually spreads over the lip of the sulcus on to the 

 lingual lobule, in the outward or surface direction, and down to the floor of the sulcus, 

 in the downward or central direction. From this the important point may be gathered 

 that the cortex clothing the upper, or more correctly speaking, the limbic wall of the stem 

 of the calcarine fissure does not possess the peculiar lamination under consideration, and 



1 In an important paper on the anatomy of the occipital region published by Dr Elliot Smith as this passes 

 through the press, these fissures and parts receive other names, thus, the stem or anterior calcarine fissure is called 

 the sulcus calcarinus projiriits, the posterior calcarine fissure with its posterior vertical subdivision the sulcus retro- 

 calcarinus (vel intrastriatus mesialis), and the field bearing the line of Gennari the area striata. 



