THE CEEEBEUM 509 



THE CEREBRUM. Frontal sections through the entire 

 breadth of the cerebrum, at the region of the thalami, show the 

 continuation of the corona radiata into the white medulla of the 

 cerebral hemispheres, the entire radiation being surrounded by the 

 grey matter of the cerebral convolutions (cerebral cortex, pallium) 

 as by a mantle. 



The white matter of the cerebral medulla, besides the many 

 fibres of the corona radiata, contains an innumerable number of 

 short fibres which bring the nerve cells of all portions of the grey 

 cortex into intimate conduction relation with each other. These 

 fibres collectively form the cerebral association paths ; the nerve 

 cells from which their fibres are derived likewise form the associa- 

 tion centers of the cerebrum as distinguished from the projection 

 centers, whose nerve fibres enter the corona radiata. 



Many of the association fibres, in their passage from center to 

 center, form definite bundles, which may be arbitrarily classified 

 into three groups. 1. Some bundles connect corresponding por- 

 tions of opposite cerebral hemispheres, e. g., corpus callosum, ante- 

 rior commissure, hippocampal commissure (fornix commissure, or 

 psalterium). 2. Some connect different lobes of the same hemi- 

 sphere, e. g., inferior longitudinal fasciculus, fronto-occipital fas- 

 ciculus, fronto-parietal fasciculus, and the superior longitudinal 

 fasciculus or fasciculus arcuatus. 3. Numerous arcuate fibres pass 

 beneath the sulci to connect the nerve cells of adjacent convo- 

 lutions. 



The nerve cells which enter into the formation of the grey 

 matter of the cerebral cortex present a remarkable tendency to 

 arrange themselves in more or less well-defined layers parallel to 

 the surface of the cerebral convolutions. The number and arrange- 

 ment of these layers in the various lobes varies, however, with the 

 peculiar function of each of these areas. Thus, in the motor area 

 there is a five layer type, in the parietal lobe a seven layer type, in 

 the occipital lobe a six or eight layer type. 



FIG. 394. SCHEME OF THE MOTOR AREA OF THE CEREBRAL CORTEX, SHOWING T.IE 

 EFFECT OF VARIOUS STAINING METHODS. 



J, Golgi's stain ; #, Weigert's stain ; ?, hematein and eosin ; 4, relative depth of each 

 layer. A, association cells ; Ag, angular cells of the polymorphous layer; As F, asso- 

 ciation fibres ; Ax, neuraxes ; <?, collateral ; C F, centripetal fibres ; E, terminal fibres ; 

 F, fusiform cell of the polymorphous layer ; <?, Golgi cells, Type II ; M, cells of Marti- 

 notti ; P C, collateral of a pyramidal cell ; Py, pyramidal cells ; Py ax, neuraxis of a 

 pyramidal cell; Py S pyramidal neuraxes passing to the cerebral medulla. (After 

 Berkley.) 



