386 DIVERGING FIBRES. 



somewhat larger above than below. The corpus olivare is situated imme- 

 diately external to the corpus pyramidale, from which, and from the corpus 

 restiforme, it is separated by a well-marked groove. In this groove some 

 longitudinal fibres are seen which enclose the base of the corpus olivare, 

 and have been named funiculi siliquce^ those which lie to its inner side 

 being the funiculus internus, and those to its outer side the furiiculus cx- 

 ternus. Besides these there are other fibres which cross the corpus olivare 

 obliquely, these are the fibrce arciformes. When examined by section 

 (Fig. 175), the corpus 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 den- 

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

 tated capsule, open behind, and containing medullary substance from which 

 a fasciculus of fibres proceeds upwards to the corpora quadrigemina and 

 thalami optici. The nervous filaments which spring from the groove 

 on the anterior border of the corpus olivare, are those of the hypoglossal 

 nerve ; and those on its posterior border are the glosso-pharyngeal 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 restiforme, 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 corresponding corpus restiforme. The processus clavati 

 are the lateral boundaries of the nib of the calamus scriptorius. The cor- 

 pus restiforme is crossed near its entrance into the cerebellum, by the au- 

 ditory- nerve, the choroid plexus of the fourth ventricle, and the pneumo- 

 gastric lobule. 



The remaining portion of the medulla oblongata visible from the exte- 

 rior, are the two slightly convex columns which enter into the formation 

 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 medulla 

 oblongata have a special arrangement on reaching the upper part of that 

 body, those of the corpora pyramidalia and olivaria enter the pons Varolii, 

 and are thence prolonged through the crura cerebri, thalami optici, and 

 ^corpora striata to the cerebral hemispheres; but those of the corpora resti- 

 formia 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 

 cruy cerebri. The "fibres of the crus cerebri again are separated in the 

 ihabrmis ODticus, and are intermingled with grey matter, and they also 



