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 "Steckel junior, it occasionally gives off a ciliary nerve, and according to "%lecke' 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 been yet established, from the spheno-palatine ganglion.
The ganglion gives off from its anterior ex tremity a considerable number of very delicate filaments, denominated from their distribution ciliary : they amount to from twelve to sixteen ; are reddish and tortuous; and run forward along the optic nerve to the back of the eye, which they enter at a short distance from the nerve. They are distinguished into two fasci culi, superior and inferior; which are attached, one to the superior anterior, the other to the inferior anterior angles of the ganglion : the former is the smaller ; contains at first hut three filaments, which, as they proceed, divide so as to produce six, and run parallel to each other above the optic nerve : the second fasciculus is situate on the outside of and beneath the optic nerve, and contains from six to ten filaments col lected at their origin into six branches: they pass beneath the nerve and incline inward, so as to gain, some of them, its inner side : one of them runs outward and joins one of the ciliary branches of the nasal nerve. The ciliary nerves all penetrate the sclerotic coat of the eye sepa rately and obliquely ; then run forward between the sclerotic and choroid coats, without giving filaments to either, lodged in channels upon the inner surface of the former : as they ap proach the ciliary circle they divide, each into two or three filaments, which enter the circle and are lost in it : some of them pierce the choroid at the anterior part of the eye, and go to the ciliary processes.
The ciliary branches are two or three in number ; they are very delicate, and are given off, while the nasal is crossing the optic nerve ; they run forward along the optic, imbedded in fat, penetrate the sclerotic coat of the eye pos teriorly, and then continue forward between the sclerotic and choroid coats, in like manner as the other ciliary nerves, to the ciliary circle.
The ityi•a-trochlear branch, so called by the elder Meckel, because it escapes from the orbit beneath the trochlea of the oblique mus cle, is also called external nasal. It is given
off when the nasal has reached the inner wall of the orbit, and as it is about to enter the fora men orbitarium ; it is a branch comparatively considerable, at times longer, at others smaller decidedly than the continuation of the nasal ; it runs directly forward along the inner wall, beneath the superior oblique muscle, toward its trochlea, and having reached that, escapes from the orbit beneath it. It then divides, in the internal canthus of the eye, into two branches, a superior and an inferior.
The infra-trochlear, while within the orbit, gives off occasionally, soon after its origin, a small branch, which returns and joins the nasal before it enters the foramen orbitarium also a delicate branch, which joins a corre sponding branch given off either by the supra trochlear or the frontal. The distribution of the nerve resulting from their junction has been already described under the frontal nerve. Of its ultimate branches, the superior joins and forms a plexus with a branch of the supra-tro chlear nerve, already described, given off either immediately before or after that nerve has escaped from the orbit. From the junction of the two, numerous delicate ramifications are distributed to the upper eyelid and to the eye brow. The inferiorgives off several ramifications, which are distributed to the origin of the cor rugator, the orbicularis, and the pyramidalis nasi muscles ; to the conjunctiva, at the inter nal canthus ; the carunculalachrymalis and the lachrymal sac. Of those ramifications, one de scends before the tendon of the orbicularis, and communicates with a branch of the portio dura : another communicates with a branch of the infra-orbital ; but the latter anastomosis is uncertain.* The nasal nerve having entered the nostril di vides at the roof of the cavity into two branches, an external and an internal: of these the former descends behind the nasal process of the frontal and the corresponding nasal bones, contained in the groove or canal observable upon their posterior surface. It escapes from beneath them at their inferior margin, emerging between it and the lateral cartilage of the nose, and then descends along the corresponding ala, superfi cial to the cartilage, and covered by the mus cles of the ala, toward the tip : as it approaches the tip, it divides into two filaments, one of which is distributed to that part, and the other to the ala. During its descent along the side of the nose it also gives off some delicate fila ments, and anastomoses with the ramifications of the nasal branches of the infra-orbital nerve and with the portio dura. It is called by Chaussier the naso-lobar : it is also generally known as the nerve of Cotionius. The second branch, as it proceeds, divides presently into two, of which one attaches itself to the septum, and descends, between the pituitary membrane and the periosteum, parallel and near to its an terior margin, as the naso-palatine of Scarpa does to its posterior as it proceeds, it furnishes ramifications to the membrane of the septum. The second attaches itself to the outer wall of the nostril, and descends, in like manner be tween the mucous membrane and the perios teum, along its anterior part, in front of the middle turbinate bone, until it reaches the an terior extremity of the inferior one : it then breaks up into branches, of which some are distributed to the convex surface of the latter bone in front, and others beneath it to the an terior part of the inferior meatus. The distri bution of the branch is very happily represented in Arnold's Icones.