TRANSVERSE AND COLLATERAL FIBRES. 



557 



The accessory fibres of the peduncular system are as follows : 



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

 continued up beneath the corpora quadrigernina, and form part of the tegmentum. 



b. The bundle of fibres on each side, named the fillet (lemniscus). This, which is 

 originally derived from the anterior column of the cord, proceeds from the olivary 

 fasciculus of the medulla oblongata, as previously described. Reinforced by fibres 

 from the corpus dentatum of the olivary body, it ascends through the back part of 

 the pons, still increasing in size. Appearing at the 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. Other fibres accessory to the peduncles take their rise in the grey matter of the 

 corpora quadrigemina (the brachia], and proceed on to the thalami. 



d. Lastly, fibres of another set, having a similar destination, are derived from the 

 corpora geuiculata. 



2. The transverse commissural, or connecting fibres of the cerebrum, include the 

 following sets. 

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



Fig. 380. 



Fig. 380. VIEW OF A DISSECTION OF TUB 

 FIBRES IN THE LEFT CEREBRAL HEMI- 

 SPHERE FROM BELOW (after Mayo). | 



The most of the middle lobe in its lower 

 part has been removed. , the anterior and 

 ', the posterior part of the fillet of the 

 corpus callosum ; b; g, section of the cms 

 cerebri ; b, tegmentum ; y, crust separated 

 from the last by the locus niger ; c', fibres 

 stretching from the back part of the corpus 

 callosum into the posterior lobe ; e, fasciculus 

 uncinatus connecting the anterior and middle 

 lubes across the Sylvian fissure ; /, /, trans- 

 verse fibres from the corpus callosum passing 

 into the cerebral hemispheres ; I, back part 

 of the thalamus ; m, corpus albicans ; q, 

 median section of the corpus callosum ; ;*, 

 radiating fibres of the hemispheres ; t, ante- 

 rior pillar of the fornix descending into the 

 corpus albicans (m) ; v, collateral fibres of 

 the convolutions ; x , anterior commissure. 



the hemispheres, some being directed up- 

 wards, whilst others spread outwards on 

 the roof of the lateral ventricles, forming 

 there what is named the tapetum. Having 

 intersected the peduncular radiating fibres, 

 they spread out into the hemispheres, 

 reaching everywhere the grey matter of the 

 convolutions. 



b. The fibres of the anterior commissure 



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

 into the middle of the hemispheres, on each side. 



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 third system of fibres in the cerebrum, the longitudinal or collateral, in- 

 cludes those of the fornix, tsenia semicircularis, and striae lougitudinales of the 

 corpus callosum, already sufficiently described ; and likewise the following. 



a. Fibres of the yyrus fornicatus ; fillet of the corpus callosum (Mayo). These 

 fibres constitute the white substance of the gyms fornicatus, and take a longitudinal 

 course immediately above the transverse fibres of the corpus callosum. In front 



