332 Dr. Foville's Researches on the Anatomx) of the Brain. 



The corpora pyramidalia anteriora are the only parts in 

 which there is an evident decussation of fibres. 



The cerebellum is the continuation of the corpus rectiforme, 

 which meeting with and confounding itself with the bundle of 

 nervous matter designated by the name of processus ad testes, 

 and with the larger bundle proceeding from the tuber annu- 

 lare, forms a mass at first somewhat rounded, but wliich soon 

 expands into a fibrous plane,which extending fi-om within out- 

 wards reaches the cineritious matter at the circumference, when 

 expanding itself both above and below into a white and very 

 fine layer, it lines the cineritious matter, accommodating itself 

 to all its folds, which are applied to the two surfaces of the 

 large plane formed by the concurrence of the three nervous 

 bundles as already mentioned. 



One part of this plane is reflected backwards from without 

 inwards towards the median line, and with its fellow forms with- 

 in the substance of the processus vermiformis a commissure 

 analogous to the corpus callosum of the cerebrum. 



Thus the three processes which constitute the crus cerebelli 

 penetrate the medullary matter of the cerebellum, and lining 

 it with a surface of white matter are enveloped by it as the 

 stem of a young champignon is by its cap. Reil had already 

 seen a part of this arrangement. 



The corpora quadrigemina receive from the medulla ob- 

 longata two bundles of fibres, which are easily traced to the 

 corpora olivaria. 



Lastly, the cerebrum receives through the intervention of 

 its crura the remaining bundles of fibres which enter into the 

 composition of the medulla. Each crus cerebri is composed 

 of two distant bundles of fibres. One of these is the continu- 

 ation of one of the anterior pyramids of the medulla oblon- 

 gata, which decussating with its fellow at the upper part, and 

 passing from behind forwards, crosses at right angles the trans- 

 verse fibres of the tuber annulare, before which they are so 

 disposed as to form a sort of groove. The posterior bundle, 

 of which I have next to speak, is lodged in this groove, and 

 completes the cylinder of the crus cerebri. 



This posterior bundle of the crus cerebri proceeding fi-om 

 the posterior part of the medulla without decussating with its 

 fellow, passes over the superior transverse fibres of the tuber 

 annulare on which its inferior surface rests, whilst its superior 

 forms the floor of the fourth ventricle. 



Throughout the whole extent of the crus properly so called, 

 these two bundles, though more and more closely approxi- 

 mating, remain nevertheless distant, being separated by a black 

 substance, the locus niger. They proceed nearly parallel to 

 each otht^r till they diverge in the corpora striata and thalanii 



nervorum 



