70 Tape of Arrangement of Nerve Fibres [CHAP. 



the interradiary plexus proper, which is striking, but the presence throughout the radiary 

 zone of an abundance of fibres of large calibre, the majority of which run horizontally or 

 obliquely ; these are seen to perfection at the lip of the Rolandic fissure, where they form 

 a coarse and rich plexus ; but further along the crown of the convolution, and also in the 

 Rolandic wall they are not so numerous. The oblique course which these fibres follow is 

 to be specially noted, because, having discovered that such fibres frequent known sensory 

 areas, e.g. the primary visual and auditory centres, I venture to assume that their obliquity 

 of position signifies that they are designed for the conveyance of centripetal impulses, and 

 that they impinge on cells deep down in the cortex. This point will again be introduced 

 when the function of this area is discussed. 



In addition to these fibres running in the plane of section many others of equal size 

 are visible, which have been cut transversely and form perfect rings, and which, therefore, 

 must be ascending the convolution in a vertical direction. 



(c) Association Fibres. 



Anatomically speaking, the large fibres just described pertain to the association system, 

 because in some part of their course they seem to occupy the position where the so-called 

 association fibres Meynert's fibrae propriae are to be sought, namely, along the margin of 

 the white substance ; hence it is impossible to pick out the latter for analysis. 



With regard to intergyral connections, I have closely examined the floor of the fissure of 

 Rolando in a great number of sections, with the view of ascertaining whether any of these 

 large, deeply-placed fibres could be traced definitely and continuously from the postcentral to 

 the precentral side, but always without success, and the conclusion I have arrived at is, that 

 if that association is consummated the path followed does not lie in the cortex; I would 

 not say, however, that the white substance immediately below the cortex does not constitute 

 the medium of conveyance, but in point of fact there is such a confusion of fibres in this 

 situation that it is impossible to trace individuals for any distance, and one cannot speak 

 definitely on the point. 



One point stands out clearly the floor of the fissure of Rolando forms a definite 

 boundary for a change in type. 



Medullary Projection. 



If a fair transverse section of the two central convolutions be inspected with the naked 

 eye, it will be at once noticed that while the outline or figure of the anterior projection is 

 stout, rounded, and voluminous, that of the posterior is thin, drawn out, and pedunculated ; 

 and another point of some importance is, that in thin transverse sections of the postcentral 

 medullary projection, numbers of large fibres, cut transversely, may be seen, and these occupy 

 a certain position, namely, the anterior half, that is to say, the half which underlies the 

 cortex just described. 



