996 
through a foramen formed by the parietal and 
interparietal bones, and runs along the whole 
length of the back on each side of the dorsal 
fins, receiving in its course filaments from all 
the spinal nerves, and giving off branches 
to the muscles and rays of the fins of the 
back. This branch is superficial up to the 
point where it plunges beneath the little ex- 
ternal muscles of the fin-rays, and it sometimes 
gives off branches which are equally superficial, 
and that descend to the muscles of the trunk 
above the pectoral fins, and others which run 
backwards as far as the anal fin, where they 
form a longitudinal nerve resembling that of 
the back. Such is the general arrangement of 
this remarkable nerve, but it is by no means 
invariably so: thus, in the Carp it seems to 
proceed from the eighth pair, and not from the 
fifth. In the Silurus, on the contrary, it ema- 
nates from the fifth alone, while in the Perch, 
Cod, &c. it is derived, as has been described, 
equally from both these sources. 
6. The sixth pair of nerves, or abducens, (fig. 
529, 6) takes its origin, as in other Vertebrata, 
from the inferior surface of the medulla oblon- 
gata, and is entirely appropriated to the external 
rectus muscle of the eye. 
7. The seventh pair of nerves (fig. 529, 7) is 
appropriated, as in other Vertebrata, to the 
sense of hearing. It arises from the medulla 
oblongata between the fifth and eighth pairs, 
and is distributed over the sacculi which con- 
tain the otolithes and the ampulle connected 
with the semicircular canals of the ear. It has 
likewise connections with the last branch of 
the fifth pair, and one which is especially con- 
stant with the glosso-pharyngeal division of the 
eighth pair of nerves. 
8. The roots forming the eighth pair (fig. 529, 
8), or nervus vagus, are collectively almost as 
large as the fifth, behind which they take their 
origin generally by numerous filaments that 
issue in a single line, that runs longitudinally 
along the sides of the medulla oblongata be- 
neath the lobes situated behind the cerebellum, 
and which unite into a ganglion (fig. 530, ¢) 
before its divisions are given off. 
The distribution of the eighth pair of nerves 
in Fishes affords a striking example of the con- 
stancy with which a nerve presides over the 
same functions in every class of vertebrate 
animals, 
The glosso-pharyngeal issues from the cra- 
nium sometimes through an aperture in the 
lateral occipital, sometimes through a foramen 
in the petrous bone, and supplies the first 
branchia and the parts in its immediate vici- 
nity, whence it passes forward to the tongue, 
in which it is ultimately expended. 
The nervus vagus properly so called leaves 
the cranium through a special foramen in the 
lateral occipital bone, and soon dilates into a 
large ganglion, from which nerves proceed to 
supply the three last branchie and the inferior 
parts of the pharynx. The trunk of the nerve 
then passes on along the pharynx and ceso- 
phagus as far as the stomach, which it likewise 
supplies. This distribution, as will be seen, 
is similar to what is found to exist in all the 
PISCES. 
vertebrate classes as far as relates to the func- 
tions over which the nerve presides, although 
its arrangement is necessarily modified in con- 
sequence of the changed position of the respi- 
ratory organs. The eighth pair of nerves gives 
off one important branch, and sometimes two, 
the relations of which with what is met with 
in the superior classes are not so apparent. 
The first oF these is a branch which arises 
sometimes from the anterior roots of the S, 
and sometimes from the posterior margin of its 
ganglion, and runs ina straight line as far as 
the tail. In many Fishes, after having given — 
off a superficial filament which follows the 
commencement of the lateral line, the trunk 
of the nerve passes straight backwards im- 
bedded in the thickness of the lateral mus- 
cles, between the ribs and their appendices, — 
receiving special filaments from every one of — 
the spinal nerves quite distinct from the inter-— 
costals, and giving off branches to the skin, — 
which pass through all the intervals between — 
the muscular layers. In other cases, as in the 
Cod-fish represented in the figure, it is super 
ficial throughout its whole course, and a= 
rently has no communication with the spinal 
nerves, although perhaps such communications 
may exist in the shape of very delicate fibrille. 
The second remarkable branch is that already 
described as joining an offset from the fifth to” 
form the dorsal nerve. a 
The eighth pair likewise gives off filaments 
to the diaphragm or membranous septum 
which divides the branchial chamber from the 
abdominal cavity. i 
The last pair of cranial nerves arises behin« 
the eighth pair from the medulla oblongata 
and, after giving a branch to the swimmin 
bladder, is distributed to the muscles of th 
shoulder, and those which pass between th 
shoulder and the hyoid apparatus ; it also git 
branches which anastomose with those of th 
first spinal nerve, and from the plexus th 
priee the nerves proceed which supply t 
external and anterior muscles of the pects 
fins. t 
The second pair of spinal nerves supply 
internal and posterior muscles of the pee! 
fins. In the Trigle ( Gurnards ) these me 
are remarkable for their great size, and o1 
count of the large branches that they give © 
the free rays situated in front of the peet 
They arise from the sides of the last of the 
pairs of post-cerebellic lobes, which in this: 
of Fishes are so remarkable. we 
In Fishes which have their pelvis suspen 
to the bones of the shoulder, whether the ¥ 
tral fins a r in front of the pectorals or 
neath hear behind them, it is from the thi 
and fourth pairs of spinal nerves that the vi 
trals receive their supply; the third speen 
supplying the muscles of the pelvis, to wl 
likewise the fourth give some branches, but 
latter is more particularly distributed to 
rays. The muscles of this fin likewi 
some filaments from the fifth pair of 
nerves. 
In the jugular division of Malacopterygin 
Fishes, in which the ventral fins are attachet 
ppa- 
