vi] Ti/jx'M of Cell Lamination 153 



Interradiary Plexus and Association Fibres (Plate XIII, fig. 3). 



The whole radiary zone has a pallid appearance because the interradiary plexus proper 

 is composed of very thin and delicate fibres, and the association system is not well repre- 

 sented. The few association fibres present are only of medium size and lie in the immediate 

 neighbourhood of the white substance, which in turn is pale-stained on account of its poor 

 fibre-wealth and especially its poverty in fibres of large calibre. 



Topical Variations. 



The various series of sections have been searched very carefully to ascertain whether 

 this large area (vide fig. 15) can be further split up on the basis of additional variations 

 in the arrangement of cortical fibres but this has been found to be impossible, because 

 although slight differences are noticeable these are merely undecided changes in density, and 

 over all the absence of fibres of large calibre is the dominant feature and has been the 

 main guide in settling the limits of the field. Special interest accrues to the discovery 

 that the angular gyrus, which is supposed to possess special functions, does not differ 

 structurally from other parts of the area (Plate XIV, fig. 2 and Plate XIII, fig. 4). 



TYPES OF CELL LAMINATION. 



It is possible to distinguish three types, but the topical variations in cell lamination 

 are not equivalent in degree to the differences in fibre-arrangement, also the intervening 

 gradations are by no means abrupt : hence the extent and limits of these types of lamination 

 are by no means easy to define; however, I may say that the following description has 

 been built up on a particularly full and careful examination of the lobe, and above all 

 things I would mention that judgments concerning the size, number, and general dis- 

 position of cells in various parts have been based not upon mere microscopic inspection, 

 but upon the comparative results given by a great number of camera lucida drawings 

 made at various magnifications. This statement is necessary because experience gained in 

 this work has proved to me over and over again that the eye cannot be trusted to make 

 reliable comparisons, especially when the matter concerns the relative magnitude, or the 

 number of given cells in different sections : accordingly when any doubt has existed on 

 these points I have always settled the matter by making a drawing; and tedious as this 

 procedure undoubtedly is, it is a very necessary, indeed an essential, safeguard in work of 

 this description. 



THE TRANSVERSE TEMPORAL GYRI. TYPE No. 1 (Plate XV, fig. 1). 



The plexiform layer calls for no special remark ; it is about '29 mm. deep. 



The average depth of the layer of small pyramidal cells is nearly '20 mm., and it is 

 noticed that the cells are very numerous and have a closely-packed appearance. This, as 

 I shall presently mention, seems to be a somewhat important feature. 



It is not easy to estimate the depth of the lamina of medium-sized pyramidal cells 

 because it merges with the succeeding layer of large pyramidal cells. But the number of the 

 C. 20 



