CH. XLIV.] 



THE SURFACE OF THE BULB. 



623 



middle line is a groove, which is a continuation upwards of the 

 anterior median fissure of the spinal cord ; the columns of the 

 bulb are, speaking roughly, continuations upwards of those of the 

 cord, but there is a considerable rearrangement of the fibres in 

 each. Thus the prominent columns in the middle line, called 

 the pyramids (a a), are composed of the pyramidal fibres, which 



Fig. 462. Ventral or anterior surface of 

 the pons Varolii, and medulla oblon- 

 gata. a, a, pyramids ; b, their decus- 

 sation ; c, e, olivary bodies ; <I, d, 

 restiform bodies ; . arcuate fibres ; 

 /, fibres passing from the anterior 

 column of the cord to the cere- 

 bellum; g. anterior column of the 

 spinal cord ; h, lateral column ; p, 

 pons Varolii ; i, it upper fibres ; 

 5, 5, roots of the fifth pair of nerves. 



Fig. 463. Dorsal or posterior surface 

 of the pons Varolii, corpora quad- 

 rigemina, and medulla oblongata. 

 The peduncles of the cerebellum 

 are cut short at the sides, a, a, the 

 upper pair of corpora quadri- 

 gemina ; b, b, the lower ; /, f, supe- 

 rior peduncles of the cerebellum ; 

 e, eminence connected with the 

 nucleus of the hypoglossal nerve ; 

 e, that of the gfosso-pharyngeal 

 nerve ; i, that of the vagus nerve ; 

 d. d, restiform bodies ; p, p, poste- 

 rior columns ; v, v, groove in the 

 middle of the fourth ventricle, 

 ending below in the calamus scrip- 

 torius ; 7, 7, roots of the auditory 

 nerves. 



in the spinal cord are situated principally in the lateral columns 

 of the opposite side (crossed pyramidal tracts). The decussation 

 or crossing of the pyramids (b) occurs at their lower part ; a 

 small collection of the pyramidal fibres is, however, continued down 

 the cord in the anterior column of the same side of the cord 

 (direct pyramidal tract) : these cross at different levels in the 

 cord. 



On the outer side of each pyramid is an oval prominence (c c), 

 which is not represented in the spinal cord at all. These are 



