MOTOR NUCLEI IN PHYLOGENY SPAR 
As in ganoids, the vagus column in teleosts extends caudally a 
considerable distance beyond the rostral end of the occipito- 
spinal motor column, and lies dorsal to this nucleus (figs. 26, 29 
and 18). 
It will be seen from the reconstruction charts in figure 40 that 
the extent of this overlap may be variable even in closely allied 
forms. In Solea, the motor X nucleus ends rostrad of the exit 
level of the first occipito-spinal rootlet, while in Hippoglossus, it 
extends a considerable distance caudad of the corresponding 
point. It is to be noted, however, that there is a much smaller 
amount of variation to be observed when the total length of the 
VII-IX—X column in these forms is compared. A similar con- 
dition is to be seen jn a comparison of the reconstruction charts 
of the siluroids Ameiurus and Silurus, though of course in this 
case it is the IX—X columns that are to be compared one with 
the other (figs. 41 A and 42 A). 
In Solea, the position of the motor X nucleus in transverse 
section is illustrated in figures 26 and 27. The motor rootlets 
of the vagus pass laterally, and emerge ventral to the descending 
trigeminal root and below their corresponding sensory root. In 
Amelurus, the relations of the motor X rootlets and of their 
nucleus of origin are illustrated in figures 28 and 29. 
It is of interest at this point to compare Bartelmez’ reconstruc- 
tion of the motor nuclei in Ameiurus melas (9, fig. 2) with my 
own chart of these relations in Ameiurus nebulosus (fig. 41 A). 
The only essential difference in the sagittal relations recorded 
in the reconstructions, lies in the position of the caudal end 
of the vagus nucleus with reference to the occipito-spinal motor 
column. In the specimen of Ameiurus nebulosus from which 
figure 41 A was prepared, the overlap of the columns in question 
was considerable; but as no such overlap is indicated by Bartel- 
mez in Ameturus melas, it is probable that there is a certain 
amount of ‘specific’ variation in the extent of this overlap— 
just as there is a considerable ‘generic’ variation in this rela- 
tion among closely allied forms (vide supra Pleuronectidae). 
If, however, the total length of the IX—X nucleus in A. melas and 
A. nebulosus be measured and then divided into the distance 
