DIVERGING FIBRES. 427 



these are ihefibra arciformes. When examined by section, the cor- 

 pus olivare is found to be a ganglion deeply embedded in the medulla 

 oblongata, and meeting its fellow at the middle line behind the corpus 

 pyramidale. The ganglion of the corpus olivare (corpus dentatum, 

 nucleus olivse), like that of the cerebellum, is a yellowish-grey denta- 

 ted capsule, open behind, and containing medullary substance from 

 Avhich a fasciculus of fibres proceeds upwards to the corpora quadrige- 

 mina and thalami optici. The nervous filaments which spring from 

 the groove on the inner side of the corpus olivare, are those of the 

 hypoglossal nerve ; and those on its outer side are the glosso-pharyn- 

 geal and pneumogastric. 



The Corpora restiformia (restis, a rope), comprehend the whole of 

 the posterior half of each lateral column of the medulla oblongata. 

 They are separated from the corpora olivaria by the grooves already 

 spoken of ; posteriorly they are divided from each other by the fissura 

 longitudinalis posterior and by the fourth ventricle, and superiorly they 

 diverge and curve backwards to enter the cerebellum, and constitute 

 its inferior peduncles. Along the posterior border of each corpus res- 

 tiforme, and marked off from that body by a groove, is a narrow white 

 cord, separated from its fellow by the fissura longitudinalis posterior. 

 This pair of narrow cords are termed the posterior median columns or 

 fasciculi (funiculi graciles). Each fasciculus forms an enlargement 

 (processus clavatus) at its upper end, and is then lost in the corre- 

 sponding corpus restiforme. The processus clavati are the lateral 

 boundaries of the nib of the calamus scriptorius. The corpus resti- 

 forme is crossed near its entrance into the cerebellum, by the auditory 

 nerve, the choroid plexus of the fourth ventricle, and the pneumogas- 

 tric lobule. 



The remaining portion of the medulla oblongata, visible from the 

 exterior, are the two slightly convex columns which enter into the for- 

 mation of the floor of the fourth ventricle. These columns are the 

 funiculi teretes or posterior pyramids. 



DIVERGING FIBRES. The fibres composing the columns of the me- 

 dulla oblongata have a special arrangement on reaching the upper part 

 of that body, those of the corpora pyramidalia and olivaria enter the 

 pons \ r arolii, and are thence prolonged through the crura cerebri, tha- 

 lami optici, and corpora striata to the cerebral hemispheres ; but those 

 of the corpora restiformia are reflected backwards into the cerebellum 

 and form its inferior peduncles. 



From pursuing this course, and spreading out as they advance, 

 these fibres have been termed by Gall the diverging fibres. While 

 situated within the pons the fibres of the corpus pyramidale and 

 olivare separate and spread out, and have grey substance interposed 

 between them ; and 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 grey matter, and they also quit that body greatly increased in 

 number and bulk. Precisely the same change takes place in the 



