MOTOR NUCLEI IN PHYLOGENY 545 
Motor vagal nucleus (Nu. mot. N. X). The position of the ros- 
tral end of the motor occipito-spinal nucleus. relative to the cau- 
dal end of the motor vagus column and to the exit level of the 
first occipito-spinal rootlet is one which is subject to a con- 
siderable amount of variation in teleosts, even among closely 
related forms (vide supra). Consequently the degree of overlap 
of the occipito-spinal nucleus and the motor vagus column in 
teleosts is not an accurate measure of the caudal extent of the 
latter nucleus. However, to estimate the relative development 
of the caudal end of the motor vagus nucleus it becomes only 
necessary to compare the total length of this structure in dif- 
ferent forms regarding the rostral end in all cases as a fixed 
point. The reason for this becomes evident when it is recalled 
that the musculature receiving its innervation from the first 
three branchial trunks of the vagus among teleosts is subject 
to but little variation in its relative development, while on the 
other hand the pharyngo-clavicularis muscles and especially 
the trapezius muscle may vary considerably both in their 
relative development and in the character of their innervation. 
A trapezius muscle which is innervated solely by the vagus 
nerve and whose homology with the muscle of this name among 
selachians can hardiy be doubted, has been demonstrated in the 
following teleosts, Salmo (Edgeworth, 20), Menidia (Herrick, 
34), Silurus (Juge, 56), Lophius (Guitel, 31) and Ameiurus 
(Herrick, 36). A trapezius muscle is absent or represented by a 
muscle innervated by spinal nerves, in the following teleosts: 
Esox, Cyprinus, Perea (Vetter, 95), and Gadus (Herrick, 35). The 
pharyngo-claviculares muscles are innervated by the vagus in 
an essentially similar manner in each of the following forms: 
Menidia, Gadus, and Ameiurus (Herrick) and in Silurus (Juge). 
Of these forms, the motor nuclei have been studied and re- 
constructed in Silurus, Ameiurus, Lophius, and Gadus, so that 
jt is possible to institute comparisons here with a considerable 
degree of accuracy (vide figs. 41 and 42). In the case of Gadus 
and Lophius, the motor vagus nucleus is completely isolated 
from the other constituents of the caudal viscero-motor column 
and it becomes at once evident that the length of the nucleus 
