560 



THE CEREBRUM. 



thick over all parts of the cortical substance, but becomes thicker as it approaches 

 the borders of the convoluted surface ; it is accordingly less conspicuous on the 

 lateral convex aspect of the hemispheres, and more so on tho convolutions situated in 

 the longitudinal fissure which approach the white surface of the corpus callosum, and 

 on those of the under surface of the brain. It is especially well marked on the 

 middle lobe, near the descending cornu of the lateral ventricle, where the convo- 

 luted surface is bounded by the posterior pillar of the fornix, and it has been there 

 described under the name of the reticulated wliite, substance. It consists of remark- 

 ably fine tubular fibres, for the most part varicose, which run parallel with the sur- 

 face of the convolutions, but intersect each other in various directions. The ter- 

 mination and connections of these fibres are unknown. This superficial white layer 

 contains also a few small cells with processes, and an abundant granular matrix. 

 2. Immediately beneath the white layer just described, is found a comparatively thick 

 layer of grey or reddish grey matter, the colour of which, as indeed of the grey sub- 

 stance generally, is deeper or lighter according as its very numerous vessels contain 

 much or little blood. Then follow, 3. Another thin whitish layer; and 4. A thin 

 grey stratum. This last lies next to the central white matter of the hemisphere. 

 Remak considers it as similar in nature to the gelatinous substance of the spinal 

 cord. According to this account, the cortical substance consists of two layers of grey 

 substance, and two of white ; but in several convolutions, especially those situated 

 near the corpus callosum, a third white stratum may be seen, which divides the 

 most superficial grey layer into two, thus making six in all, namely, three grey and 

 three white. 



Fig. 3 S3. 



Fig. 383. MINUTE STKUCTUKK OF THE CEREBRAL SUBSTAKO ; (from Kolliker), MAGNIFIED 



220 DIAMETERS. 



A, cells and structural elements from the inner part of the cortical substance of the 

 cerebral convolutions ; a, larger cells, chiefly from the middle grey layer, showing a 

 variable number of radiating processes; b, smaller cells from the more superficial grey 

 layer, in part belonging to connective tissue; c, a nerve-fibre with its axis-filament 

 partly exposed. 



B, finest nerve-fibres from the superficial wliite layer of the cortical substance of a 

 convolution, some showing the varicose condition. 



The cortical grey substance consists of nerve-cells of rather variable size, which are 

 angular, fusiform, round, or oval in shape, and for the most part caudate, and lie in a 

 granular matrix; also of small nucleus-like vesicles, which resemble those seen in 

 the cortical substance of the cerebellum, and, according to Todd, are here also 

 collected into a special stratum. In the middle grey layer, the cells are of variable 

 gize, some being so small as to resemble nuclei ; but others of much larger dimen- 

 sions are abundant, and, according to Kolliker, present from one to six processes. 



