14 General Remarks on Cortical Fibre Arrangement [CHAP. 



and is largely responsible for the depth of colour, noticeable in the radiary field, when it is 

 examined under a low power of the microscope. 



Its constituents bear subdivision into, first, an intricate meshwork of fibres of delicate 

 calibre, the course of which it is impossible to trace for any distance and which are probably 

 collaterals of projection fibres ; and secondly, long coarse fibres which run obliquely or trans- 

 versely and weave themselves in among the radiary bundles. It seems correct to assume 

 that the latter pertain to the association system, and that the term interradiary plexus should 

 be applied and confined to the plexus of delicate fibres. 



I .shall have occasion to mention that the interradiary plexus is subject to instructive 

 variations in density in different parts of the cortex. 



Association Fibres of Meynert. 



" Bogen Systeme " or Laminae Arcuatae of Arnold. By this we understand the system 

 composed of fibres of considerable size and great length, situated within the radiary zone, 

 running in arcuate fashion round the white projection and intersecting the radiary fasciculi 

 at right angles. The system is always easy to identify along the floor and walls of sulci 

 and just as difficult to follow round the convexity of the gyrus. 



Many writers describe the system as consisting of an external and an internal layer, 

 the latter being named the fibrae propriae of Meynert, but to my mind the differentiation 

 is an artificial one and uncalled for. Along the walls and floor of sulci the fibres form a 

 compact and solid lamina, which it is impossible to split up, and, as Kaes correctly describes, 

 in their course upwards the innermost fibres gradually become incorporated with the radiary 

 fasciculi and so cease to exist as a transverse layer ; the outermost fibres, on the other hand, 

 are not interrupted in this manner, but arch in the form of a continuous band round the 

 summits of the radiations at the level of, and above and below, the line of Baillarger, with 

 which they are more or less incorporated. 



According to Vulpius the fibres of this system do not attain their full development until 

 after the 17th year, and Kaes states that they are seen at their best in the most highly 

 evolved parts of the brains, but to this I shall return later. 



From Vulpius' paper we gather that the fibres were recognised by Remak in 1840, again 

 mentioned by Arndt in 1868, and further described by Exner, Tuczek, Fuchs, Edinger, Vignal, 

 Henle, Meynert, etc., but none of these observers seem to have discovered adequate reasons 

 for gracing the system with a physiological title. 



Feltwork or Filz of Kaes. 



This may be described as the dense plexiform arrangement along the margin of the 

 white substance, which results from the fusion of the association and projection fibres. 



White or Medullary Projection. 



This term is employed in describing the appearance which the white substance presents 

 in a transverse section of a gyrus ; it of course projects upwards more or less in the form 

 of a sugar loaf. 



