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The large sensory root gradually conceals the small motor root in its course forwards, and expands beneath the dura mater into a large flattened ganglionthe semilunar ganglion. This ganglion occupies an impression on the apex of the petrous portion of the temporal bone, and from it three large trunks arise-the ophthalmic or first, the maxillary or second, and the mandibular or third divisions of the nerve. The small motor root of the nerve passes forward beneath the ganglion, and is incorporated wholly with the mandibular division of the nerve.
The ophthalmic nerve passes forwards to the orbit through the middle fossa of the skull, in the dura mater. It lies in the lateral wall of the cavernous sinus, at a lower level than the trochlear nerve, and reaches the orbit through the superior orbital fissure (Fig. 645).
FIG. 648.-DISTRIBUTION OF SENSORY NERVES TO
In the wall of the cavernous sinus the ophthalmic nerve gives off (1) a small recurrent branch to the dura mater (n. tentorii), (2) communicating branches to the cavernous plexus of the sympathetic on the internal carotid artery, and (3) small communicating twigs to the trunks of the oculo-motor, trochlear, and abducent nerves.
In the superior orbital fissure the nerve divides into three main branches-lacrimal, frontal, and naso-ciliary (Fig. 645).
N. Lacrimalis. The lacrimal nerve enters the orbit through the lateral angle of the superior orbital fissure, above the orbital muscles. It passes forwards, between the periosteum and the orbital contents, to the anterior part of the orbit, and ends by supplying branches (a) to the lacrimal gland, (b) to the conjunctiva,and (c) to the skin of the lateral commissure of the eye.
The lacrimal nerve communicates in the orbit with the zygomatic branch of the maxillary nerve, and on the face, by its terminal branches, with the temporal branches of the facial nerve (Fig. 653).
N. Frontalis.-The frontal nerve enters the orbital cavity through the superior orbital fissure, courses forwards above the ocular muscles, and divides at a variable point into two branches-a larger supra-orbital and a smaller supratrochlear nerve.
N. Supraorbitalis.-The supraorbital nerve passes directly forwards, and leaves the orbit through the supra-orbital groove or foramen to reach the forehead. It gives off the following secondary branches: (1) the principal (frontal) branches (rami frontales) are distributed to the forehead and scalp, reaching backwards as far as the vertex; (2) small branches supply the upper eyelid; and (3) twigs are
distributed to the frontal sinus. On the forehead the supra-orbital nerve communicates with the temporal branches of the facial nerve.
N. Supratrochlearis.-The supra-trochlear nerve courses obliquely forwards and medially above the tendon of the superior oblique muscle to reach the medial side of the supra - orbital arch, where it leaves the cavity of the orbit; it is distributed to the skin of the medial part of the forehead, the root of the nose, and the medial commissure of the eye.
It communicates with the infra-trochlear branch of the naso-ciliary nerve, either before or after leaving the orbital cavity.
N. Nasociliaris.-The naso-ciliary nerve (O.T. nasal) enters the orbit through the superior orbital fissure, between the heads of the lateral rectus muscle, and between the two divisions of the oculo-motor nerve (Fig. 652, p. 776). It crosses the orbital cavity obliquely to reach the anterior ethmoidal foramen, lying in its course below the superior rectus and superior oblique muscles, and above the optic nerve and medial rectus muscle. The nerve is transmitted, under the name of anterior ethmoidal, through the anterior ethmoidal foramen into the cranial cavity, where it lies embedded in dura mater on the lamina cribrosa of the ethmoid bone. It enters the nasal cavity through the nasal fissure, and terminates by dividing into medial and lateral branches. The medial division supplies the mucous membrane over the upper and anterior part of the nasal septum. The lateral branch, after supplying collateral offsets to the lateral wall of the nasal cavity, finally appears on the face as the external nasal nerve between the nasal bone and lateral cartilage, and supplies branches to the skin of the lower part and tip of the nose.
The branches of the naso-ciliary nerve may be divided into three sets, arising (a) in the orbit, (b) in the nose, and (c) on the face.
In the orbit the branches are given off in three situations-lateral to, above, and medial to the optic nerve. (a) As the nerve lies on the lateral side of the optic nerve, it gives off the radix longa ganglii ciliaris (long root of the ciliary ganglion). (b) As it crosses above the optic nerve, nn. ciliares longi (two long ciliary branches) arise, and pass forwards alongside the optic nerve to the eyeball. (c) On the medial side of the optic nerve the n. infratrochlearis (infra-trochlear nerve) arises, a slender branch which courses forwards below the pulley of the superior oblique muscle to the front of the orbit. It ends on the face by supplying the skin of the root of the nose and the eyelids, and communicates either in the orbit or on the face with the supra-trochlear nerve. On the face it also communicates with zygomatic branches of the facial nerve.
In the nose the rami nasales mediales (medial nasal branches) supply the mucous membrane of the anterior part of the nasal septum; the rami nasales laterales (lateral nasal branches) supply the anterior part of the lateral wall of the nasal cavity.
On the face the terminal filaments of the nerve are distributed, as the ramus nasalis externus (external nasal branch), to the skin of the lower half and tip of the nose. The terminal branch communicates with the zygomatic branches of the facial nerve (Fig. 653).
Ganglion Ciliare. The ciliary ganglion is associated with the naso-ciliary branch of the ophthalmic nerve and with the inferior division of the oculo-motor nerve. It is a small reddish ganglion, placed between the lateral rectus muscle and the optic nerve, and in front of the ophthalmic artery. Its roots are three in number: (1) sensory or long, derived from the naso-ciliary branch of the ophthalmic nerve; (2) motor or short, derived from the inferior division of the oculo-motor nerve; and (3) sympathetic, a slender filament from the cavernous plexus on the internal carotid artery, which may exist as an independent root or may be incorporated with the long root from the naso-ciliary nerve. The branches from the ganglion are twelve to fifteen nn. ciliares breves (short ciliary nerves), which pass to the eyeball in two groups above and below the optic nerve. They supply the coats of the eyeball, including the iris and ciliary muscles. The circular fibres of the iris and the ciliary muscle are innervated by the third nerve the radial fibres of the iris by the sympathetic.
The Maxillary Nerve. This large nerve courses forwards from its origin in the semilunar ganglion through the middle fossa of the skull, in the dura mater, and in relation to the lower part of the cavernous sinus (Fig. 647, p. 771). It passes through the foramen rotundum, traverses the pterygo-palatine fossa, and enters the orbit as the infra-orbital nerve, through the inferior orbital fissure. In the orbit it occupies successively the infra-orbital groove and canal, and it finally appears on the face through the infra-orbital foramen (Fig. 653).
The branches and communications of this nerve occur (a) in the cavity of the cranium, (b) in the pterygo-palatine fossa, (c) in the infra-orbital canal, and (d) on the face.
In the cavity of the cranium the nerve gives off a minute (n. meningeus medius) middle meningeal (O.T. recurrent nerve) to the dura mater of the middle fossa of the skull.
In the pterygo-palatine fossa the nerve gives off (1) two short thick sphenopalatine nerves, the sensory roots of the spheno-palatine ganglion.
(2) Posterior superior alveolar nerves, which may be double, descend through the pterygo-maxillary fissure to the lateral side of the maxilla, and proceed forwards along the alveolar arch, in company with the posterior superior alveolar artery. They supply the gum and the upper molar teeth by branches which perforate the bone to reach the alveoli. The nerves form a fine plexus joined by the middle alveolar nerve before finally reaching the teeth.
(3) A small zygomatic (O.T. orbital) branch enters the orbital cavity through the inferior orbital fissure, and proceeding along the lateral wall, communicates
with the lacrimal nerve, and passes through the zygomatico-orbital foramen in the zygomatic bone, where it divides into two branches. The zygomatico-facial (O.T. malar) branch appears on the face, after traversing the zygomatic bone, and supplies
Nerves to superior rectus and
FIG. 652.-SCHEMATIC REPRESENTATION OF THE NERVES WHICH TRAVERSE THE CAVITY OF THE ORBIT.
the skin over that bone. It communicates with the zygomatic branches of the facial nerve. The zygomatico-temporal (O.T. temporal) branch perforates the temporal surface of the zygomatic bone, and is distributed, after piercing the temporal fascia,
Nerve to rectus medialis from oculo-motor
Zygomatico-facial branch Inferior palpebral branch External nasal nerves Infra-orbital nerve, leaving canal External nasal branch
FIG. 653.-THE COURSE OF THE OPHTHALMIC AND MAXILLARY NERVES.
to the skin over the anterior part of the temple. It communicates with the temporal branches of the facial nerve. It may be very minute, and not pass further than the temporal fascia, between the two layers of which it may form a communication with the facial nerve.