When there is a second palpebral branch, it takes the place of the external branch of tho former, which in such case is denominated the internal inferior palpebral, and the second the external. It perforates the levator labii supe rioris muscle ; ascends toward the external angle of the eye, beneath the othicularis palpe brarum ; and, like the external branch of the inferior palpebral, already described, supplies the structure of the lid, and anastomoses with the portio dura, lachrymal, and rnalar nerves, as also with the internal palpebral.
The descending or labial branches are the largest and the most numerous ; for the most part they are three, at times four. They de scend to the upper hp, one toward its middle, the second toward its intermediate, and the third toward its outer part, the commissure of the lips, and are denominated internal, mid dle, and external ; they are situate, all at first, beneath the levator labii superioris, between it and the levator anguli oris or canine muscle; as they descend, they give filaments to these muscles and to the parts superficial to them ; and they pass to their several destinations, the internal between the levator labii and the de pressor aim nasi ; the middle between the same muscles ; and the external superficial to the levator anguli, and uncovered by the levator labii ; as they approach the lip they divide each into branches, which are distributed to the structures of the part at their several situa tions ; to the orbicularis oris, and the insertions of the other muscles of the lip, to the integu ment of the lip, internal and external, and also to the labial glands ; they all communicate to gether, and with branches of the portio dura; the external more particularly with the latter, as also with the neighbouring branches of the fifth ; the internal with the inferior nasal; the external with the inferior labial and buccal nerves. In the infraorbital region, the branches of the superior maxillary are crossed by and interlaced with those of the portio dura; the latter running from without inward, and for the most part superficial to the former ; but also beneath and among them, and even forming loops about them ; while the former run from above downward, and are principally deeply seated. In consequence of this diversity in their directions and the numerous anastomoses which they hold with each other, the branches of the two nerves form a very intricate mesh in that region.
In some Carnivora filaments of the facial branches of the fifth nerve have been traced into the bulbs of the hairs of the whiskers and the tufts with which they are furnished ; this is remarkably so in the seal, as described by Andml : they are strongly expressed by Rapp.* The internal or nasal branches are, for the most part, two; they are termed superficial nasal by the elder Meckel, and distinguished into supe rior and inferior; they pass, both, inward toward the nose, beneath the levator labii superioris, the inferior at the same time descending, and having reached the side of the nostril they sub divide.
The superior is the smaller of the two, and arises frequently from a branch common to it and the internal inferior palpebral ; it divides into three, of which the first, the uppermost, is distributed to the origin of the levator lahii alteque nasi, to the compressor naris, and to the integuments on the dorsum of the nose ; the second, the middle, to the compressor naris and also to the integuments of the nostril, and the third, the inferior, to the compressor naris, to the depressor aloe nasi, and to the integu ments of the ala.
The inferior superficial nasal, the larger of the two, first gives occasionally a branch, which ascends to the eyelid ; then communicates with the superior, and having reached the ala of the nose, it gives off numerous ramifications which are distributed to the levator and depressor aim, to the integuments of the inferior part of the ala, of the tip, and of the septum, and also to the upper lip ; it communicates with the rami fications of the naso-lobar branch of the nasal nerve, of the internal labial, and of the portio dura.
The third division of the fifth.—This trunk has been denominated by Winslow, on account of its general distribution, the inferior maxillary nerve, and it is generally known by that appel lation ; yet it appears to the writer that it would have been much better had that title been applied only to that portion of the nerve which enters the lower jaw. Such is the opinion of the elder Meckel, who observes that this use of the epithet leads to the inconveni ence that the branch alluded to and the trunk of the nerve may be easily confounded. It is much the largest of the three divisions, and differs remarkably from the other two in its composition ; they are both single, and derived altogether from the Gasserian ganglion ; it on the contrary is composed and made up of two portions, one derived from the ganglion, the other not connected with it ; the former is the largest of the three trunks connected with the ganglion ; it is attached to its posterior external extremity ; at its attachment it is cineritious and very wide, but as it proceeds it loses that tint, and acquires a compressed cylindrical form. It is situate external, posterior, and in ferior to the others, and its course within the cranium is very short or none, for from the ganglion it enters at once the inferior maxillary or foramen ovate of the sphenoid bone, and escapes from the cavity, passing downward, for ward, and outward, nearly at right angles with the second division of the fifth. Before leaving the cranium it is joined, as the first and second divisions are, by a filament from the sympa thetic, according to Munniks, Laumonier, and Bock.* The second portion, of which the third division is composed, is the lesser packet of the fifth itself; this, it has been already stated, does not join the ganglion, but passing out ward, beneath that body, is united to the former portion posteriorly, in the foramen ovate ; it forms, however, but a small proportion of the nerve, that part which is attached to the gan glion exceeding it very much in size. At its junction, it is placed posterior to the other, but it immediately spreads out, and increases very much in width, and at the same time is lapped round the inner side of the ganglionic portion so as to get before it, and to form the anterior part of the nerve by the time it has escaped from the cranium.