CHAP, ii.] 



THE BRAIN. 



751 



cc. the rostrum of the corpus callosum, 8pl. 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 Reil and the operculum or convolution overlapping the island 

 of Keil. 



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



ishes and disappears, through fibres leaving it to cross over to the 

 other side by the anterior commissure. During its progress 

 along the spinal cord, the fibres both of the crossed and the 

 direct tract end by coming into connection with the cells of the 

 anterior cornu, either by means of their collaterals or by their act- 

 ual terminations. In the bulb and higher up, the tract gives off 

 fibres which crossing over to the other side make connections in 

 a similar way with nerve cells whose axis cylinder processes are 

 motor fibres in the cranial nerves. From these relations of the 

 pyramidal tract it is obvious that the fibres of this tract must be 

 concerned in the development of the movements which we have 



brack 



FIG. 126. OUTLINE OF A SAGITTAL SECTION THROUGH THE HEMISPHERE. Man. 



(Sherrington.) 



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 thalanms is 

 shaded. 



2Vc, 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, fron., a pyramidal 

 system, PY (sub-divisible into cranial [craw.], 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. CB, 

 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. 



