32 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



On looking at Fig. 6, we should expect that on removing 

 another layer we should find the hemispheres separated from 

 the ventricle only by a thin layer of epithelium. This, however, 

 is not the case. At a later period of embryonic development, 

 thick masses of fibres have developed and pass from one hemi- 

 sphere to the other at a point shown by the letter a in Fig 6. 



Sim 



Ccl 



FIG. 18. 



Fore-brain from above. The hemispheres have been removed at the level of the 

 corpus callosum (Ccl). The white space between Ccl and the cortex is the centrum semi- 

 ovale. Lt, ligamentum tectum or striae longitudinales Lancisi, a part of the cortex 

 which borders on the corpus callosum. mm, striae longitudinales mediales, white 

 bundles of fibres which interlace on the'middle of the corpus callosum. ^After Henle.) 



Thus, at the bottom of the great fissure we do not find the ven- 

 tricle, but the corpus callosum, as the mass of transverse fibres 

 is called. 



The corpus callosum is now divided, and after the white 

 substance which lies over the ventricles on each side has been 

 removed it is cut off before and behind. Then it is seen that 



