120 



NERVOUS SYSTEM 



arched the corpus striatum becomes highly bowed, surrounding the hemisphere- 

 stalk and extending from the rhinencephalon in front (future locus perforate 

 anticus) to the extremity of the temporal horn (fig. 158). As the body is pro- 

 longed backwards into the tail it overlaps the thalamus, but is necessarily 

 separated from it by the cleft between thalamus and hemisphere (see fig. 150). 

 This cleft is obliterated from below, as thalamus and corpus striatum 

 enlarge, by a fusion of the two bodies, associated with the fusion of th< 

 ependymal infrachoroidal lamella of the mesial hemisphere-wall with th( 



I 



FIG. 164. SECTION THBOUGH THE SAME BRAIN AS IN FIGS. 162 AND 163, MUCH NEARER THE BASE. 



(T. H. Bryce.) 



The section now cuts the mid-brain M. The diverticula on each side of III, placed in the cavity 

 the third ventricle, are the rudiments of the geniculate bodies ; H, H, the temporal horns of the hemi- 

 sphere-vesicles with the tail of the corpus striatum. The notch on the outer surface of each hemisphe 

 opposite rf is the sulcus marking off the rhinencephalon on the lateral aspect of the brain ; Ilia is 

 placed in the fore and basal part of the third ventricle. Immediately in front (above in the figure) of 

 Ilia is the lamina termmalis, here thickened. In front of the lamina terminalis are two triangul 

 fields (trapezoid areas), separated by a narrow cleft occupied by a delicate prolongation of the primitive 

 falx. In front of this the falx is much broadened out, and angular projections from it occupy the 

 fissures primse. The cavity of the hemisphere-vesicle is at this level interrupted by the union of the 

 projection corresponding to the fissura prima with the lateral crus of the corpus striatum (see 

 figs. 162, 163). The anterior pocket is the mouth of the cavity in the olfactory stalk. 



outer side of the thalamus (fig. 162). The hemisphere-stalk is thus greatly 

 enlarged, and in the tissue between the thalamus and corpus striatum the 

 capsule takes form first, by the formation of the thalamus bundle connecting 

 that body with the hemisphere (fig. 163) ; and later by the addition of the 

 pyramid-fibres connected with the crus cerebri. 



It may here be pointed out that while the outer reticular zone in the spinal cord becomes the 

 white covering, this zone remains quite a thin layer on the hemisphere, and the white matter is 



