CHAP. IL] THE BRAIN. 993 



abundant; this, and the occurrence of various bundles of fibres, 

 gives the region great complexity ; and we must confine ourselves 

 here to touching on one or two important longitudinal strands 

 which traverse it. 



The superior peduncle of the cerebellum is one of the most 

 important of these. This is on each side a bundle of fibres which, 

 taking origin chiefly from the grey matter of the nucleus dentatus, 

 and the smaller neighbouring collections of grey matter, but also 

 in part from the superficial grey matter, leaves the cerebellum in 

 front of, and to the median side of the restiform body and passes 

 forward towards the corpora quadrigemina to converge with its 

 fellow. At first the two peduncles are superficial and dorsal in 

 position (Figs. Ill, 112, S.P.) and the space between them is 

 bridged over by the valve of Vieussens (Fig. 112, Via) ; but, still 

 converging, they soon sink ventrally beneath the posterior corpora 

 quadrigemina and at the level of the junction between the anterior 

 and posterior corpora quadrigemina meet and decussate ventral to 

 those bodies in the ventral region of the tegmentum (Fig. 113, 

 S.P.). Beyond the decussation they are continued forwards in the 

 tegmentum ventral to the anterior corpora quadrigemina as two 

 strands, one on each side, which appear to end in the red nuclei. 



In this way the peduncles connect certain parts of the grey 

 matter of the cerebellum with the tegmental region, and more 

 particularly with the red nucleus, and thus indirectly with the 

 structures with which that region is itself, connected. 



The fillet. This, as we have seen ( 612), takes origin in the 

 bulb, in the interolivary layer between the inferior olives, from 

 fibres which are derived through the supra-pyramidal or sensory 

 decussation from the gracile and cuneate nuclei. From this 

 origin it passes forward on each side as a flat band into the 

 tegmental region of the pons, receiving accessions from the superior 

 olive and other collections of grey matter, and dividing there into 

 two strands, the median (Figs. 112, 113, Fm) and lateral (Figs. 

 112, 113, Fl and Fig. 108, BF) fillet. The lateral division ends 

 partly in the grey matter of the posterior corpus quadrigeminum, 

 and partly in the white matter underlying (Fig. 114, dm) the 

 anterior corpus quadrigeminum ; the median division passing 

 farther forward appears partly to end in the grey matter of the 

 anterior corpus quadrigeminum, but partly to be continued on to 

 the subthalamic region of the tegmentum ventral to the thalamus, 

 thence to the thalamus, and so to the cortex. 



The longitudinal posterior bundles. In a transverse section 

 through the fore part of the pons at the level of the posterior 

 corpora quadrigemina a rather conspicuous bundle of longitudinal 

 fibres (called the longitudinal posterior bundle) is seen on each 

 side, cut transversely, in the dorsal region of the tegmentum just 

 ventral to the nucleus of the fourth nerve (Fig. 113, I). Traced 

 backward from the aqueduct beneath the fourth ventricle, it 



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