THE BASAL GANGLIA 



29 



interpeduncular fossa (p. 16) and, posteriorly, by the grooved 

 upper surface of the mid-brain. The roof is formed by the 

 tela chorioidea (velum interpositum) and, above that, by the 

 fornix and the corpus callosum (Fig. 14). 



The Basal Ganglia are masses of grey matter, which are 

 more or less completely embedded in the substance of the 

 brain near its basal surface. Their cells act as cell-stations 

 for both afferent and efferent fibres of the cerebral cortex. 



Optic tract 



Lateral geniculate body 



Medial geniculate body 

 Pulvinar 



Corpora quadrigemina 



Mid-brain 



-Corpus mamillare 



HL Trigeminal nerve 



FIG. 17. The Lateral aspect of the Brain-Stem. 



The basal ganglia comprise (i) the thalamus, and (2) the 

 corpus striatum, which is further subdivided into the caudate 

 and the lentiform (lenticular) nuclei. 



i. The Thalamus lies directly above, and is continuous 

 with, one-half of the peduncle of the mid-brain, but projects 

 beyond it both anteriorly and posteriorly. When viewed 

 from above, it is seen to be somewhat triangular in outline 

 and its postero-medial angle shows a distinct enlargement, 

 which is termed the pulvinar. The postero-lateral angle, 

 which overhangs the lateral aspect of the mid-brain, possesses 



