590 MANUAL OF HISTOLOGY. 



of the two halves of the cerebellum as commissural systems, they conduct 

 no new fibres into the interior of the organ, but, on the contrary, convey 

 fasciculi of nerve fibrils springing from the cerebellum further upwards into 

 the cerebrum. 



Now, it seems very improbable that the whole mass of fibres conveyed 

 through the first-named crura into the cerebellum, terminate provision- 

 ally there, to escape again through another set of processes by the last- 

 named crura. It is far more likely that only a portion of the mass 

 takes this circuitous route through the cerebellum, while the rest passes 

 directly into the cerebrum. Thus we have in the cerebellum a most com- 

 plicated accessory apparatus. Its abscision, moreover, in keeping with 

 this view, disturbs certain connections to a great extent, but does not 

 completely put an end to them. 



The blood-vessels of the medulla oblongata have the same arrangement 

 as those of the spinal cord. 



As elsewhere, the white substance found in the medulla oblongata is 

 traversed by an open network of capillaries, whose elongated meshes are 

 seen according to the direction of the fibres, either in profile, or in trans- 

 verse section. The collections of grey matter, on the other hand, are 

 much more vascular, and supplied by a denser interlacement of capillaries. 

 The very closely intercommunicating capillaries of the cineritious capsule 

 of the human olivary bodies present a peculiarly beautiful appearance ; 

 they are partly supplied by vessels from without, and partly by another 

 set of larger tubes, situated in the white nuclei. We shall speak of the 

 lymphatics further on ( 300) in their proper place. 



298. 



Turning from the medulla oblongata to the neighbouring parts of the 

 brain, we find that less and less is known of their structure the farther 

 we advance. 



In the foregoing section we have had frequent occasion to touch upon 

 many points relating to the pons Varolii and cerebellum, so that they 

 may now be first described. 



In regard to the pons Varolii we have already remarked, in the pre- 

 ceding section, that in it we have before us collections of grey matter 

 with the white cords of the medulla passing through it. Further, it con- 

 tains a series of well-marked transverse fibres. 



The cerebellum consists essentially of collections of white nervous 

 tissue, cineritious matter only presenting itself on the roof of the fourth 

 ventricle, in the corpus dentatum, the so-called roof nucleus of Stilling, 

 and in the layer covering the surface of the convolutions. 



Into and out of it, as we know, the crura cerebelli ad medullam conduct 

 bands of fibres of the medulla oblongata. In the same way further ele- 

 ments leave it through the (297) crura cerebelli ad pontem. Finally, the 

 crura cerebelli ad corpora quadrigemina connect the organ with the brain. 



The whole of the cerebellum presents, likewise, that very delicate sus- 

 tentacular connective-tissue alread}' mentioned ( 119). It is especially 

 highly developed in the cortical layer. 



The nerve fibres of the white substance of the cerebellum are stated to 

 present a similar arrangement and diameter at almost all points ; the 

 latter is, on an average, 0'0045, but may range from 0'0027 to 0'0902 

 mm. (Koelliker). 



The cineritious substance is only to be found, in small amount, on the 



