556 THE CEREBRUM. 



a. The superior peduncles of the cerebellum (processus ad cerebrum), 

 which are continued up beneath the corpora quadrigemina, and form part 

 of the tegmentum. Some of these fibres are believed by Mejnert to 

 be connected with the cells of the corpus striatum. 



&. The bundle of fibres on each side, named the filht (lemniscus) 

 (/, fig. 387). This, which is originally derived from the anterior column 

 of the cord, proceeds from the olivary fasciculus of the medulla oblon- 

 gata, as previously described. Reinforced by fibres from the corpus 

 dentatum of the olivary bod}^, it ascends through the back part of the 

 pons, still increasing in size. Appearing at tlie side of the cerebral 

 peduncle, above the upper border of the pons, it divides into two portions, 

 •of which one crosses over the superior peduncle of the cerebellum to the 

 corpora quadrigemina, meeting its fellow of the opposite side, while 

 the other is continued upwards with the fibres of the tegmentum. 



c. Fibres from the middle peduncles of the cerebellum are believed to 

 turn upwards in the pons and join those of the crusta. (Meynert, 

 Broadbent.) 



d. The crusta also contains fibres which pass upwards from the 

 grey nuclei in the floor of the fourth ventricle. 



e. Other fibres accessory to the peduncles take their rise in the grey 

 matter of the corpora quadrigemina (constituting their hrachia), and 

 proceed on, the anterior to the thalami optici and surface of the inner 

 ■corpora geniculata ; the posterior to the inner corpora geniculata and 

 thence to the crura cerebri. 



/. Lastly, fibres of another set, also joining the peduncles, are de- 

 rived from the corpora geniculata. 



2. The transverse commissural or connecting fibres of the cere- 

 brum, include the following sets. 



a. The cross fibres of the corpus callosum pass laterally into the 

 substance of. the hemispheres, some being directed upwards, whilst 

 others spread outwards on the roof of the lateral ventricles, forming 

 there what is named the iapchmi. Intersecting the peduncular ra- 

 diating fibres, they spread out into the hemispheres, reaching every- 

 where the grey matter of the convolutions. In the middle of the white 

 centre of the hemisphere the ascending fibres preponderate, but 

 gradually disappear towards the corpus callosum, while, on the other 

 hand, towards the convolutions all the fibres assume an ascending 

 'direction, and the decussation disappears. It is doubtful whether any 

 of the ascending fibres of the corona radiata enter the corpus callosum. 



T). The Jibres of the anterior commissure, exceedingly fine, pass laterall}' 

 into the corpora striata, and bending backwards, extend a long way 

 into the middle of the hemisphere, and are distributed to the temporo- 

 sphenoidal lobes (fig. 388 x ). 



c. The fibres of the posterior commissure run through the optic 

 thalami, and are soon lost in the substance of the hemispheres outside 

 these bodies. 



3. The longitudinal or collateral system of fibres includes those 

 of the fornix, ta}nia seniicircularis, and strife longitudinales of the corpus 

 callosum, already sufficiently described ; and likewise the following. 



a. Fibrr,^ of the gyrus fGrnicatus ; fillet of the corpus callosum (Mayo). 



-These fibres constitute the white substance of the gyrus fornicatus, 



and take a longitudinal course immediately above the transverse fibres 



of the corpus callosum (fig. 389, a a'). In front they bend downwards 



