Immediately after their escape the frontal branches give off externally slender filaments, which run outward toward the external can thus, one beneath the eyebrow, through the upper eyelid, and one or more through the brow itself; these ramify as they proceed, sup ply the lid and brow at their outer part, and anastomose with filaments of the portio dura, and of the superficial temporal nerve.
The frontal branches are arranged into super ficial and deep ; those epithets have been diffe rently applied by different writers ; thus those which the elder Meckel terms the superficial, Boyer and Cloquet denominate the deep branches ; nor is this to be wondered at, inas much as both sets become ultimately superficial; it were better, perhaps, to arrange them into short and long branches. The short branches are distributed to the orbicularis muscle, the corrugator, and the frontalis, and having sup plied those muscles, they or others of them be come subcutaneous, and terminate in the inte gumeots 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 periera 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 "'Steckel 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 Scemmerring. 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 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 palpebral, the 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-troehkar, and the nasal.