ANATOMICAL STRUCTURE 



535 



as the fasciculus of Rolando. In the upper portion of the medulla the gracile, 

 cuneati, and Rolandic fasciculi are replaced by the restiform bodies (the in- 

 ferior peduncles of the cerebellum). The lateral columns of the cord are 

 scarcely represented as such in the bulb. 



It may be said then that the bulb at its commencement differs only slightly 

 in size from the cord, with which it is continuous. It soon becomes larger 

 both laterally and antero-posteriorly. It opens out on the dorsal surface into 

 a space which is known as the fourth ventricle, and from being a cylinder with a 

 central canal it is flattened out on the dorsal surface by the gradual approach 

 of the central canal to that surface, where it is directly continuous with the 

 fourth ventricle. 



If the bulb be examined on its anterior or ventral surface, it is found that 

 the anterior fissure, which is a continuation of the same fissure in the cord, is 



FIG. 374. 



FIG. 375. 



FIG. 374. Ventral or Anterior Surface of the Pons Varolii and Medulla Oblongata. a, a, An- 

 terior pyramids; b, their decussation; c, c, olivary bodies; d, d, rjestiform bodies; e, arciform 

 fibers; f, fibers passing from the anterior column of the cord to the cerebellum; g, anterior col- 

 umn of the spinal cord; h, lateral column; p, pons Varolii; i, its upper fibers; 5, 5, roots of the 

 fifth pair of nerves. 



FIG. 375. Dorsal or Posterior Surface of the Pons Varolii, Corpora Quadrigemina, and Me- 

 dulla Oblongata. The peduncles of the cerebellum are cut short at the side, a, a, the upper 

 pair of corpora quadrigemina; b, b, the lower; f, f, superior penduncles of the cerebellum; c, 

 eminence connected with the nucleus of the hypoglossal nerve; e, that of the glosso-pharyngeal 

 nerve; i, that of the vagus nerve; d, d, restiform bodies; p, p, posterior pyramids; v, v, groove in 

 the middle of the fourth ventricle, ending below in the calamus scriptorius; 7, 7, roots of the audi- 

 tory nerves. 



occupied at the most posterior part by fibers which are crossing from one side 

 to the other. This is what is known as the decussation of the pyramids. It is 

 formed of the fibers which occupy the postero-lateral region in the cord, and 

 are called the crossed pyramidal fibers. The lateral pyramidal fibers of either 

 side after crossing the middle line become part of the pyramid of the opposite 

 side; the rest of the pyramid is made up of the fibers which in the anterior 



