986 



THE FIBRES OF THE BRAIN. 



[BOOK HI. 



front of the pyramidal tract, run almost horizontally, parallel with the plane 

 of the section. Cf. Fig. 122, Fran. 



cc. the rostrum of the corpus callosum, Spl. the splenium of the same, both cut 

 across horizontally. The thick dark line indicates the boundary of the 

 cavities of the anterior and descending horns of the lateral ventricle and of 

 the third ventricle, the two ventricles being laid open into one by the removal 

 of the velum and choroid plexus &c. The oval outline in the fore part of this 

 cavity indicates the fornix. 



Lateral to the nucleus lenticularis is seen in outline the claustrum, the cortex of 

 the island of Keil and the operculum or convolution overlapping the island 

 of Reil. 



P is inserted to shew which is the hind part of the section. 



The fibres of the brain as a whole may be broadly classified 

 into longitudinal tracts connecting parts of the brain with suc- 

 ceeding parts and into transverse or commissural tracts between 

 one lateral half and the other, and into tracts connected with the 

 several cranial nerves. Taking the longitudinal fibres first we 

 may in accordance with the division just explained into a pedal 



dors.lura, 



FIG. 122. OUTLINE OF A SAGITTAL SECTION THROUGH THE HEMISPHERE. 



(Sherrington.) 



Man. 



The section is taken not far to the right of the median plane and is one half linear 

 of natural size. The grey matter of the corpus striatum and thalamus is 

 shaded. 



Nc, Nc, the caudate nucleus ; Pt, the putamen and Gp, the globus pallidus of the 

 lenticular nucleus; OT, the optic thalamus; CI, the internal capsule with 

 a streaked appearance revealing approximately the direction taken by fibre- 

 bundles passing into it from the portion of corona radiata over it. In these 

 sets of bundles may be broadly distinguished a frontal system, /ron, a pyrami- 

 dal system, PY (sub-divisible into cranial (cran.), brachial (brack.), dorso-lumbar 

 (dors, lum.), and lumbo-sacral (lum. sac.), parts) and a temporo-occipital system. 

 sens.; the situation of the genu of the internal capsule is indicated by g. CR, 

 the crus cerebri ; Oc, the so-called optic radiations passing into the occipital lobe ; 

 cc, the splenial end of the corpus callosum ; v, v, v, the lateral ventricle cut 

 across in three different places; F, the fornix in cross-section; Op, the optic 

 tract in cross-section. Part of the cerebellum is seen in outline to the right. 



