THE MEDULLA OBLONGATA AND BRAIN. 227 



substance a peculiarly folded leaf (corpus dcntatum) which 

 encloses white substance. 



The former substance contains small yellowish pigmented 

 ganglion cells. A system of fibres arising from the olivary 

 bodies is said to pass in part to the cerebellum, in part to the 

 cerebrum. 



The crura cerebelli ad medullam oblongatam form in part 

 processes of the medulla oblongata into the cerebellum ; they 

 probably also send motory fibres from the latter in a down- 

 ward direction to the medulla oblongata (Meynert). 



The crura cerebelli ad pontem are of an essentially different 

 nature. They form in the first place a transverse commissure 

 system between both the cerebellar hemispheres ; then they 

 conduct fibrous masses, arising from the cerebellum, up to the 

 cerebrum. 



The cerebellum can, however, absorb only a portion of the 

 fibrous masses which ascend from below, and subsequently, 

 after the passage of gray substances, sends them off trans- 

 formed to the cerebrum. It is merely — as we must at present 

 assume — an accessory conducting apparatus ; for the other 

 fibrous masses ascend directly through the pedunculi cerebri. 



The blood-vessels of the medulla oblongata remind us of 

 those of the spinal cord. 



We know very little indeed concerning the cerebellum. We 

 have already mentioned two of its crura ; a third commissure, 

 the crura cerebelli ad corpora quadrigemina, connects the 

 organ with the cerebrum. 



The cerebellum consists essentially of aggregations of white 

 nerve substance, with fibres 0.0029 to 0.0902 mm. broad. 

 Gray substance occurs in the roof of the fourth ventricle, in 

 the corpus dentatum, in Stilling's so-called roof nucleus, and 

 as the external covering layer of the convolutions. 



In the folded gray plate of the corpus dentatum lie ganglion 

 cells in a threefold stratum. We pass over the entirely un- 

 certain course of the fibres. 



The structure of the cortical layer is interesting. It presents 

 an internal rust-brown, and an external gray stratum. 



