DIVERGING FIBRES. 381 



interposed between them; and that they quit the pons much increased 

 in number and bulk, so as to form the cms cerebri. The fibres of 

 the crus cerebri again are separated in the thalamus opticus, and 

 are intermingled with gray matter, and they also quit that body 

 greatly increased in number and bulk. Precisely the same change 

 takes place in the corpus striatum, and the fibres are now so extra- 

 ordinarily multiplied as to be capable of forming a large proportion 

 of the hemispheres, viz., the whole of the lower part of the anterior 

 and middle lobes. 



From observing this remarkable increase in the white fibres, 

 apparently from the admixture of gray substance, Gall and Spurz- 

 heim considered the latter as the material increase of formative 

 substance to the white fibres, and they are borne out in this conclu- 

 sion by several collateral facts, among the most prominent of which 

 is the great vascularity of the gray substance ; and the larger pro- 

 portion of the nutrient fluid circulating through it, is fully capable 

 of effecting the increased growth and nutrition of the structures by 

 which it is surrounded. For a like reason the bodies in which this 

 gray substance occurs, are called by the same physiologists "ganglia 

 of increase," and by other authors simply ganglia. Thus the 

 thalami optici and corpora striata are the ganglia of the cerebrum ; 

 or, in other words, the formative ganglia of the hemispheres. 



Mr. Solly, in a recent work upon " the human brain," has desig- 

 nated the diverging fibres of the corpus pyramidale that pursue the 

 course above described, " the cerebral fibres ;" to distinguish them 

 from another set of fibres discovered by that gentleman, which also 

 proceed from the corpus pyramidale, and pass outwards beneath the 

 corpus olivare to the cerebellum. These he names the " arciform 

 fibres" and divides them into two layers, the superficial cerebellar 

 and deep cerebellar fibres. They join the corpus restiforme, forming 

 one-fourth of its whole diameter, and spread out in the structure of 

 the cerebellum. 



The Corpora olivaria owe their convex olive-shaped form to a 

 "ganglion of increase" (the anterior ganglia of the medulla oblongata 

 of Solly), situated in the interior of each. 



The white fibres surrounding these ganglia form a fasciculus at 

 each side, which is continued into the pons Varolii along with the 

 corpora pyramidalia. Here its fibres are mixed with gray matter, 

 and pass into the crus cerebri, forming its superior and inner seg- 

 ment. From the crus cerebri they traverse successively the lhalamus 

 opticus and corpus striatum, and become developed into the convolu- 

 tions of the upper part of the hemispheres and posterior lobe. 



The Corpora restiformia diverge as they approach the cerebellum, 

 and leaving between them the cavity of the fourth ventricle enter 

 the substance of the cerebellum, under the form of two rounded 

 cords. These cords envelope the corpora rhomboidea, or ganglia 

 of increase, and then expand on all sides so as to constitute the 

 cerebellum. 



In addition to the diverging fibres which are thus shown to con- 



