126 THE POCKET ANATOMY 



The corpus dentatum, or ganglion of the cerebellum, is a 

 dentated capsule of grey matter enclosing white substance, 

 situated in the middle of the white matter of the hemisphere. 

 It is open at its anterior part, whence white fibres issue, 

 passing to the superior peduncles and valve of Vieussens. 



Nucleus emboliformis : covering hilum of corpus den- 

 tatum. 



Nucleus globosus : placed on the inner side of the preceding, 

 but at a lower level. 



Nucleus fastigii : in the anterior part of the white centre of 

 the vermiform process. 



The arrangement of white and grey matter in the cere- 

 bellum gives on section an arborescent appearance, the arbor 

 vita. 



THE MESENCEPHALON. 



The Sylvian aqueduct (iter a tertio ad quartum ventriculum) 

 is about ^ inch long. Posteriorly it is continuous with the 

 narrowed upper end of the 4th ventricle, and anteriorly it 

 opens out into the 3rd ventricle. It has a ciliated epithelial 

 lining, and outside this a layer of grey matter, both being 

 continuous with corresponding parts of the 4th ventricle. 

 Laterally and below are the crura cerebri, whilst posteriorly 

 is the lamina quadrigemina bearing the corpora quadri- 

 gemina. 



The grey matter of the aqueduct contains the nuclei of 

 the 3rd and 4th nerves, and the upper nucleus of the 

 5th nerve. 



The crura cerebri extend from the upper border of the 

 pons, and, diverging, pass under the optic tract into the 

 cerebral hemispheres. Between the crura is the interpedun- 

 cular space, containing the posterior perforated spot, the cor- 

 pora albicantia, pituitary body, infundibulum, and the tuber 

 cinereum. Near the angle of divergence the roots of the 3rd 

 nerve issue from a groove on the inner side, which groove 

 indicates the separation of the ventral part (crusta or pes 

 pedunculi) from the dorsal portion (tegmentum) of the 

 crus. 



There is a layer of grey matter placed between the pes 

 pedunculi and the tegmentum, known as the substantia nigra 

 or locus niger. 



The pes, or crusta pedunculi, consists of longitudinal white 

 fibres, of which the middle third are continuous with the 

 anterior pyramid of the medulla, and pass to the internal 

 capsule. 



