CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
747 
nerve that emerges through the vertebral column. It may be looked upon as the second 
spinal nerve, or if the first is considered to be two nerves this would be the third. 
The trunk formed by the union of these nerves constitutes a sort of brachial plexus, 
and supplies the muscles of the pectoral fin, after having given off a branch which runs 
down the anterior edge of the shoulder-girdle towards the muscles surrounding the 
glossohyal bone. 
This nerve is certainly a spinal nerve, as far as its origin goes, for it has both dorsal 
and ventral roots, and in this species it appears to be a combination of two nerves, as 
is shown by its four roots, and by its trunk dividing into two and joining again. In 
some other species — the Scorpcenci Porous, for instance — this nerve gives a branch 
which is distributed quite as far as the anterior part of the glossohyal. 
In examining a dissection of the nerves from the upper surface one is struck with 
the resemblance between the trifacial, the vagus, and the spinal nerves, in respect to 
their dorsal branches. Thus we find that in proceeding from behind forward these 
branches are given oft’ at a gradually decreasing distance from their ganglia ; in the 
spinal nerves their dorsal branch is given off distad of the ganglion ; in the first 
spinal nerve and the vagus it comes off from the ganglion itself, and in the trifacial it 
divides from the main trunk proximad of the ganglion. 
In the Whiting ( Merlangus vulgaris) the arrangement of the three nerves in 
relation to each other differs more from that of the M. Pollachius than would be 
supposed possible in species of the same genus. In this species, the so-called facial 
of Stannius arises in common with the remainder of the trifacial ; being the penul- 
timate root of that nerve, it passes over the casserian ganglion as a distinct cord 
without in any way communicating with it. It then emerges through the foramen 
with the remaining branches of the trifacial; after that, it receives the branch from 
the ganglion of the so-called glossopharyngeal, which is well developed in this species ; 
it then divides into two branches : one pursues its course along the posterior and outer 
edge of the orbit ; the other, after perforating the palato- quadrate arch, passes down 
on the outside of that structure to disappear from view outside the quadrate bone. 
The acusticus does not send a communicating branch to the vagus, but its jmsterior 
cord is closely applied to the anterior root of the latter, until it arrives at the ampulla 
of the posterior semicircular canal, when it leaves its companion to be distributed on 
that structure. The two trunks are very easily separated from each other, and there 
is no nervous connexion between them. 
In this species both roots of the vagus pass through the ear cavity over the otolithic 
sac : a disposition which is caused by the extreme backward prolongation of the latter. 
The so-called glossopharyngeal, or branch to the first branchial arch, is given off by 
the posterior root of the vagus immediately before its junction with the anterior root 
of that nerve ; it passes forward along the inner surface of the outer wall of the ear 
cavity, and emerges through the foramen in that wall, outside of which it forms the 
ganglion, as in M. Pollachius. From this ganglion the nerve for the first branchial 
