299 



(occipito-) spinal rootlets and the VII, which is easily explained by the 

 above mentioned absence' of the IX (and the greater part of tlie X ?) 

 and the caudo-frontal compression of the oblongata that results from 

 this. 



If we compare in transverse sections the position of the V — VII 

 column in Peti'omyzon (fig. 3) and Myxine (fig. 4) we find that the 

 position of this nucleus in Myxine is a much • more ventral one. 



N.L.A 



N. VI 11 



N. Vll m 



N. Vll 



nucl VII in. 



Fis. 3. VII nuclei and root of Petromyzon. 



^S ^ JU: 



SiCet^'y 



In Myxine the fairly large cells of this column are located in the 

 most ventral part of the oblongata closely against the fibres of the 

 descending V'^^ . Similarly as in Petromyzon the V^'^ and VIP^' nucleus 



