THE MEDULLA OBLONGATA AND PONS VAROLII. 461 



lie nerves (all but the first and second pairs) rise from these and 

 the crura cerebelli. . It is not consistent, however, with the object of 

 this work to describe their complicated structure at length. A 

 section of the former is shown by Fig. 305. 



1. The white substance of the medulla oblongata is in part continu- 

 ous with that of the cord, and partly distinct from it ; and everywhere 

 consists of nerve-fibres of the same dimensions as those of the cord. 

 The anterior columns of the cord (Fig. 306) are partly continued 

 into the outer part of the corpora pyramidalia ; and partly ascend 

 both internally and externally to the olivary body, and proceed 

 through the pons Yarolii into the posterior corpora quadrigemina 

 on the one hand and the tegmentum of the crura cerebri on the 

 other. The lateral columns divide, on reaching the medulla, into 

 three branches; (1,) ascending mostly into the crura cerebelli, and, 

 in small part, into the tegmentum; (2,) decussating in two or three 



Fig. 306. Fig. 307. 



Fig. 306. Anterior view of the medulla oblongata. p, p. Corpora pyramidalia decussating at d. 

 o, o. Olivary bodies, r, r. Restiform bodies, a, a. Arciform fibres, v. Lower fibres of the pons 

 Varolii. 



Fig. 307. Posterior view of the medulla oblongata. p, p. Posterior pyramids, separated by the 

 posterior fissure, r, r. Restiform bodies composed of (c, c) posterior columns, and (d, d,) lateral. 

 a, a. Olivary columns as seen on the floor of the fourth ventricle, separated by () the median fis- 

 sure, and crossed by some fibres of origin of (n, ri) the seventh pair of nerves. 



fasciculi with that of the other side (decussatio pyramidum), and 

 forming the principal bulk of the anterior pyramids ; and (3,) ap- 

 pearing between the posterior columns at the bottom of the fourth 



