FIFTH PAIR OF NERVES.
281
guments of the eyebrow and forehead : one
of these branches, as described by Meckel,
runs outward, through the orbicularis, toward
the external canthus, and establishes anasto¬
moses with filaments of the facial portio dura
nerve. The long branches are two, an external
and an internal ; of those the external is, for
the most part, the larger ; they ascend beneath
the frontalis and the frontal aponeurosis, the
former inclining outward, the latter inward, as
they ascend ; they distribute in their course
ramifications to the muscle, and to the deeper
structures of the scalp, as well as some¬
times, according to Meckel, to the pericra¬
nium, and traversing the frontal aponeurosis,
they become subcutaneous, and terminate in
the structure and integument of the scalp. The
external communicates with the superficial
temporal nerves ; the internal with the internal
frontal, the supra-trochlear. They are said both
to anastomose with the branches of the sub-
occipital nerve; but Meckel states that he
has pursued them until they have escaped
his sight, and yet he could not discover any
anastomoses between them and the branches of
that nerve.
2. The nasal nerve is in size the second
branch of the first division of the fifth, and arises
always separately from the original trunk. Its
course is inferior and internal to those of the
other two, and hence the nerve is called by
some the inferior, by others the internal branch.
It is distributed partly to the eye and its appen¬
dages and partly to the nostril, and hence it is
also called naso-ocular by Sœmmerring. The
direction of its course is forward and very
much inward ; it passes through the foramen
lacerum into the orbit ; then traverses that re¬
gion from without inward toward its internal
wall, and having reached it at the foramen or-
bitarium internum anterius, it escapes from the
orbit through that foramen, and passes into the
cranium ; it emerges into the cranium from
beneath the margin of the orbitar process of the
frontal bone, and crosses the cribriform plate of
the ethmoid obliquely forward and inward,
contained in a channel in the bone, and in¬
vested by the dura mater, until it reaches the
crista galli ; it then descends from the cranium
into the nostril, through the cleft, which exists
at either side of the crista galli at the anterior
part of the cribriform plate, and having reached
the roof of the nostril, it divides into its final
branches.*
The nasal branch is concealed at its origin
by the frontal, which is situate external and
superior to it. Before its entrance into the orbit
it is placed by the outer side of and closely ap¬
plied to the third nerve. In entering the orbit
* The nasal is usually described as terminating
by dividing within the orbit into two branches, the
ethmoidal or internal nasal, and the infra-trochlear or
external nasal ; the author has preferred considering
the former as the continuation of the nerve, be¬
cause in inferior animals both the nasal is the prin¬
cipal portion of the first division of the fifth, or
alone constitutes it, and it is manifestly prolonged,
as such, into the nostril and the beak. See Com¬
parative Distribution.
it passes between the two posterior attachments
of the external rectus muscle, in company with
the third and sixth nerves, external to the
former and between its two divisions, and
internal and somewhat superior to the latter.
In its course across the orbit the nasal nerve
passes above the optic nerve, immersed in fat,
and accompanied by the ophthalmic artery,
being at the same time beneath the levator
palpebræ, ihe superior oblique, and superior
rectus muscles, and in crossing the optic
nerve, it is placed between it and the last
mentioned muscle. Through the foramen or-
bitarium the nerve is accompanied by the an¬
terior ethmoidal artery, and within the cra¬
nium is situate beneath but not in contact
with the olfactory bulb, being separated from
it by the dura mater. The course of the nerve
from the orbit to the nostril is liable to be
modified by the developement of the frontal
sinuses ; when they are very large, and extend,
as they not unfrequently do, into the orbitar
processes of the frontal bone and the horizontal
plate of the ethmoid, the nerve may cross to
the side of the crista galli without entering the
cranium, being contained in a lamella of the
ethmoidal bone. The nasal branch, before
entering the orbit, receives, according to Bock,
J. F. Meckel, and Cloquet, a filament from
the sympathetic. The branches which the nasal
gives off, are the lenticular, the ciliary, the
infra-trochlear, and the nasal.
The lenticular branch is given off as the nasal
enters the orbit, and on the outer side of the
optic nerve; it is a delicate branch, about half
an inch long; it first anastomoses with the supe¬
rior division of the third nerve ; then runs for¬
ward along the outer side of the optic nerve,
and terminates by joining the superior and pos¬
terior part of the lenticular ganglion. Accord¬
ing to Bock and Meckel junior, it occasionally
gives off a ciliary nerve, and according to
Meckel senior it is, in rare instances, derived
from the third nerve. To the latter statement,
however, the author hesitates to assent : it ap¬
pears to him, that it should rather be said in
such cases to be wanting.
The ophthalmic, lenticular or ciliary ganglion,
according to Cloquet, is of an oblong form—
its greater length from behind forward ; it is
one of the smallest ganglia of the body,
being, however, variable in size ; its colour is
reddish, at times white ; it exists constantly in
the human subject : it is situate between the
external rectus muscle and the optic nerve, laid
against the outer side of the nerve, at a little
distance from its entrance into the orbit ; its
external surface convex, corresponding to the
muscle ; its internal, concave, to the nerve ; to
its superior posterior angle is attached the len¬
ticular twig of the nasal branch of the first
division of the fifth ; this filament constituting
its long root ; to its inferior posterior angle a
filament from the inferior division of the°third
nerve is attached, constituting its short root.
To the posterior part of the ganglion are also
attached two filaments derived, one from the
cavernous ganglion or the carotid plexus ; the
other, the constant existence of which has not