DISSECTING MANUAL. 



it forms nuclei, a network (formatio reticularis), and a layer 

 about the central canal. [489] 



PONS VAROLII. 



This is a convex white prominence above the medulla 

 which, except the restiform portion, it enters and mostly passes 

 through. The ventral surface consists of transverse white 

 fibres which are gathered on each side in a bundle (middle 

 cerebellar peduncle) ; it is convex and presents a mesial groove 

 between prominences produced by the pyramidal tracts. The 

 fifth nerve emerges laterally, nearer the upper than the lower 

 border, between the pons and middle peduncle. At the low r er 

 border the sixth nerve emerges at the outer border of the pyra- 

 mid, the seventh just in front of the restiform, and the eighth 

 on the ventral aspect of the restiform. [486] 



The dorsal surface presents the upper half of the floor of the 

 fourth ventricle, and the superior cerebellar peduncles; the 

 latter converge in ascending, finally overhanging the floor, 

 and pass under the inferior corpora quadrigemina to the 

 mid-brain. [486] 



Internal Structure. The larger ventral part consists chiefly 

 of superficial transverse white fibres (middle peduncles), of 

 longitudinal deep white bundles (pyramidal tracts) passing to 

 the crura cerebri, and of gray nuclei (pontis) between them. 

 The tegmental (dorsal) part consists chiefly of gray matter 

 (nuclei and formatio reticularis) , partly of longitudinal white 

 bundles (superior peduncles and nerve roots). [499] 



FOURTH VENTRICLE. 



This is a rhomboidal cavity bounded by the superior pe- 

 duncles above, and the clavse, cuneate tubercles and restiform 

 bodies below; it is continuous with the central canal and 

 Sylvian aqueduct. A narrow prolongation (lateral recess) 

 curves outward, from each lateral angle, around the upper part 

 of the restiform body. [487] 



[28] 



