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HANDBOOK OF PHYSIOLOGY. 



partly in fasciculi traversing the central gray matter. The medulla 

 oblongata is larger than any part of the spinal cord. Its columns are 

 pyriform, enlarging as they proceed toward the brain, and are continu- 

 ous with those of the spinal cord. Each half of the medulla, therefore, 

 may be divided into three columns or tracts of fibres, continuous with 

 the three tracts of which each half of the spinal cord is made up, the 

 columns more prominent than those of the spinal cord, and separated 

 from each other by deeper grooves. The anterior, continuous with the 

 anterior columns of the cord, are called the anterior pyramids, and the 



Fig. 358. 



Fig. 359. 



Fig. 358. 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, restiforin bodies; e, arciform 

 fibres; /, fibres passing from the anterior column of the cord to the cerebellum; gr, anterior col- 

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

 fifth pair of nerves. 



Fig. 359. 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; 6, 6, the lower; /, /, superior peduncles of the cerebellum; c, 

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

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

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

 auditory nerves. 



postero-median and postero-external columns are also represented at the 

 posterior or dorsal aspect of the cord as the fasciculus gracilis and the 

 fasciculus cu neatus. The posterior pyramids of the medulla which in- 

 clude these two columns of white matter soon become much increased 

 in width by the addition of a new column of white matter outside the 

 other two which is known as the fasciculus of Rolando. The lateral col- 

 umns of the cord undergo considerable change and are scarcely repre- 

 sented 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 



