263 



4. A line of Baillarger, definable as a dark streak lying some distance below the outer margin 

 of the radiary zone, and on a corresponding level with the Betz cells. 



A final curious point is, that on the walls of the crucial sulcus where the Betz cells are 

 abundantly deposited, and where one would expect a corresponding richness of fibres, the supply 

 is not so good as on the surrounding free surface. 



l>i.*t i-ilintliin. (Vide Plates la and ~2n.) 



In the primate brain we found the area covered by the cells of Betz of small extent, so 

 it is again in the cat. On the mesial surface, the area is confined to a small portion of the 

 marginal gyrus, situated immediately behind the sulcus cruciatus, and it is worthy of mention that 

 it does not reach quite to the hinder extremity of the sulcus. In a frontal view, the close relation 

 to the sulcus cruciatus is better displayed (as previously stated, the distinguishing cortex coats 

 both walls of the sulcus, and this, of course, cannot be shown in a surface diagram) ; then, 

 anteriorly, the area extends downwards and outwards, to be limited in turn by the upper extremity 

 of the orbital and the anterior extremity of the coronal sulcus. Laterally, the sulcus coronalis 

 constitutes a bar, transverse sections showing that the formation reaches to the floor of, but not 

 beyond this sulcus. Posteriorly, the field meets the postcrucial or sensory area midway across the 

 hinder limb of the sigmoid gyrus, and it is most important to observe that the boundary line 

 is constantly related to a shallow depression, placed equidistant from the cruciate and ansate sulci. 

 This depression varies in representation in different brains and even in opposite hemispheres ; it 

 may appear as a short transverse tissuret, or merely be a dimple, but it is never entirely absent, 

 and I have little doubt that it is the equivalent of a fissuret, better developed in other animals 

 and known as the "compensatory ansate 1 ." Further reference will be made to this fissure when 

 the homology of the part is discussed. 



VISUAL AREA. 

 Filti'i 1 Arrnitijeiiifiit. 



Many of the characters, which served for the identification of the visual area in man and 

 the anthropoid ape, are reproduced. 



The zonal layer, while better developed than in surrounding parts, is not so dense as in the 

 motor region. It is chiefly composed of fine varicose elements, but evenly-medullated fibres, of 

 rather large size, are occasionally seen, also fibres from the supraradiary layer run up to end in 

 it (fibres of Martinotti). 



The succeeding supraradiary layer is pallid, poorly supplied with fibres in its upper two-thirds, 

 but richer towards the line of Gennari. 



The line of Gennari, vel Baillarger, was our surest guide to the localisation of the visual 

 cortex (visuo-sensory) iu primates, and, again, it does not fail us in these lower animals ; in 

 general composition, moreover, it is unaltered ; but it must be pointed out that, by reason of the 

 reduced scale of construction, it is impossible to see the line with the naked eye and define its 

 area of location in unstained sections, as can be done in the human brain. 



Below the line of Gennari comes a pallid stripe, corresponding in position with the large nerve 

 cells to be presently mentioned. 



The radiary zone is again characteristic ; the bundles of Meynert are fairly stout, and are 

 often strengthened by a large medullated fibre ; and it is a point of importance that the inter- 

 radiary spaces are crossed obliquely by numerous stout fibres springing from the white substance, 

 which can only be the terminals of the radiations of Gratiolet (the optic fibres of Ramon y Cajal). 



Generally speaking, the visual cortex is rich in fibres, but wanting in depth. 



1 I have taken this name from the Royal College of Surgeons' Catalogue, compiled by Dr Elliot Smith. 



