Chap, xviii.] CEREBRUM AND CEREBELLUM. 161 



211. The cms cerefori of each side consists of an 

 antero-inferior, middle, and postero-inferior portion. 

 The antero-inferior or ventral portion is the crusta, or 

 pes ; the postero-inferior or dorsal portion is the teg- 

 mentum. Between the two is the substantia nigra. 

 The crusta is composed of longitudinal tracts of me- 

 dullated nerve-fibres passing from the margin of the pons 

 Varolii to the internal capsule of the thalamencephalon, 

 and farther into the white matter of the hemisphere. 



212. The tegmentum has been mentioned above 

 as being situated in front of the grey matter forming 

 the anterior wall of the aqueductus Sylvii. The 

 tegmentum is a prolongation of the reticular formation 

 of the pons Varolii and medulla (see above), i.e., small 

 masses of grey substance separated by tracts of nerve- 

 fibres, most of which run in a longitudinal or transverse 

 direction. The longitudinal bundles include a con- 

 tinuation of the white matter of the cerebellum, 

 mentioned in a previous page as the superior peduncle 

 of the cerebellum, or the pedunculus cerebelli ad 

 cerebrum. These undergo total decussation. in the 

 upper part of the mesencephalon, and ultimately enter 

 the thalamus opticus. 



213. The siibstantia iiigra is grey matter 

 situated between the two crusta and the tegmentum ; 

 it has received its name from the numerous dark 

 pigment granules lodged in the substance of its gan- 

 glion cells. These are small and multipolar. 



214. Y. The thalamencephalon and corpus 

 striatuin. The former comprises the parts of the 

 brain situated round the third ventricle, the most im- 

 portant being the thalamus, the conarinm or pineal 

 body, the corpora albicantia, the infundibulum and 

 tuber cinereum, and the pituitary body or hypophysis 

 cerebri. The corpus striatum is the ganglion of the 

 cerebral hemisphere, and like it originates from the 

 frontal part of the first cerebral vesicle of the embryo. 



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