STRUCTURE OF THE FIBROUS SUBSTANCE. 555 



the whole surface of the convolutions, and collected in distinct masses in certain of 

 the deeper part, such as the corpora striata, thalami optici, corpora quadrigemina, 

 and crura cerebri. To the grey substance, the names of cineritious and cortical have 

 been applied ; to the white that of medullary. 



1. The white matter of the encephalon consists of tubular fibres, in general still 

 smaller than those of the cord, and more prone to become varicose. The general 

 direction which these follow is best seen in a brain that has been hardened by 

 immersion in alcohol, although it is true that in an ordinary dissection of such 

 hardened masses with the scalpel, we do not then trace the single fibres, but only 

 the smaller bundles and fibrous lamellae which they form by their aggregation. It must 

 also be admitted that were they intimately decussate, the tearing of fibres across is 

 liable to be mistaken for the separation of sets of fibres one from the other ; and it 

 is necessary to correct such errors by the examination of sections under the micro- 

 scope. The microscopic examination of the cerebrum, however, is as yet still less 



Fig. 378. 



Fig. 378. SKETCH OP A DISSECTION SHOWING THE CONNECTION OP THR COLUMNS OP THE 

 MEDULLA OBLONGATA WITH THE CEREBRUM AND CEREBELLUM (from Mayo), i 



In the lower part of the figure the medulla oblongata is entire where it is prolonged 

 downwards into the spinal cord ; a, the anterior pyramid ; a', its continuation upwards 

 into the pons Varolii (m) ; c, olivary body ; cf, olivary fasciculus ; behind c', the fasciculi 

 teretes are represented ; d, the white laminae in part of the cerebellum ; /, superior 

 peduncle of the cerebellum ; y, anterior part or crust of the cerebral peduncle ; h, part 

 of the fibres radiating from the peduncle into the right cerebral hemisphere, of which a 

 considerable extent is shown containing parts of the anterior, middle, and posterior lobes ; 

 Ji, y, y, part of the corona radiata ; h' (in front), central fibres of the convolutions ; i, 

 fillet; I, back of the thalamus opticus ; m, pons Varolii; n, inferior peduncle of the 

 crus cerebelli ; o, section of the pes hippocampi ; r, tegmentum ; y, y, show the white 

 fibres issuing from the corpus striatum. 



complete than that of the spinal marrow and medulla oblongata. By the dissection 

 of artificially prepared brains, aided in part by microscopic observation, the following 

 general facts have been ascertained. 



The fibres of the cerebrum, though exceedingly complicated in their arrange- 

 ment, and forming many different groups, may be referred to three principal 

 systems, according to the general course which they take, viz. : 1. Ascending or 



o o 2 



