526 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



on the left side.) It now only depends upon the breadth of 

 the posterior columns situated between the posterior cornua 

 whether the radii of the posterior cornua moving in the area 

 of the circle formed by the transverse section of the medulla 

 oblongata, can accomplish the approximation found in the cord 



Fig. 260. 



Fig. 260. Transparent transverse section of the lower half of the 

 medulla oblongata of Man, at the level of the upper part of the decus- 

 sation of the pyramids. C, central canal ; P, internal and median, 

 and P', external fasciculi of the transverse section of the pyramids ; G, 

 gelatinous substance in the tuber cinereum of Rolando ; H, posterior 

 column ; Cn, nucleus of the fasciculus cuneatus ; Ghr, nucleus of the 

 fasciculus gracilis ; Oi, internal accessory nucleus ; xn, roots of the 

 hypoglossal nerve ; D, decussation of the external fasciculi of the 

 pyramids which at If curve round the tissue adjoining the central 

 canal to reach the funiculi graciles and cuneati ; A A, fibrse arcuatae 

 which are continuous with the tissue around the posterior columns, 

 but not with the pyramids ; V, the anterior column. 



to the third radius formed by the posterior fissure. And now, 

 because (figs. 258, 260, 261) the great breadth of the posterior 

 columns above depends, not on the size of its fasciculi, but 

 upon the presence of the grey masses associated with the 



