The posterior consists of several long slen der filaments, which continue to descend im mersed in the fat of the zygomatie fossa, until they reach the surface of the buccinator muscle; they then in part are distributed to it, but in greater number pass between the fibres of the muscle and are lost in the mucous membrane of the mouth.
The anterior branch descends for some time, until it reaches the back of the maxilla ; it then enters a canal in the bone, within which it is transmitted forward through the wall of the antrum; after a short way it escapes from the canal and continues its course forward within the wall, between it and the lining membrane, describing a curve convex down ward ; having reached the front of the antrum it ascends and terminates by joining either the anterior superior dental or a branch of that nerve.
During its course around the antrum the anterior branch of the nerve gives off down ward numerous delicate filaments, which de scend toward the teeth, traverse the structure of the alveolar arch, and in part are distributed to the roots of the posterior superior teeth in a manner analogous to that of the inferior dental nerves : in part they escape inferiorly from the alveolar arch between the sockets of the teeth, and are consumed in the gums. The nerve is also stated to give filaments to the membrane of the maxillary antrum.
4. Shortly before its escape from the infra orbital canal, but at a distance somewhat variable from it, the second division of the fifth gives off its next regular branch, the anterior superior dental : this descends, from the infraorbital canal, through one of its own name in the anterior wall of the antrum to ward the canine tooth ; it next runs inward above the root of that tooth, and then again descends through the perpendicular process of the maxillary bone, until it reaches the floor of the nostril, and is continued inward through the horizontal process of the bone above the roots of the incisor teeth.
While descending through the wall of the antrum the anterior superior dental nerve either is joined by the termination of the anterior branch of the posterior dental, or it divides into two, one of which inclines outward and joins that branch, the other pursues the course of the nerve. It supplies the anterior teeth of the upper jaw in the same manner as the pos terior nerve does the posterior teeth ; it also gives at its termination filaments to the mem brane of the nostril, and one to the naso palatine ganglion or nerve.
Besides the regular dental nerves, others at times arise from the second division of the fifth within the infraorbital canal, and take the place of branches of the regular nerves.
5. branches of the second division of the fifth are from five to seven in number ; they differ from each other in size, and branch off in different directions; they are distin guished, according to the direction in which they run and their destination, into three sets; a superior or palpebral, an inferior or labial, and an internal or nasal.
For the most part there is but one superior or palpebral branch, though sometimes there are two. This branch is destined to supply the lower eyelid, and is denominated the inferior polpebral nerve ; it presents some variety in its mode of origin and its course ; most frequently it does not separate from the trunk till after the latter has escaped from the infraorbital foramen; but in some instances it does so within the in fraorbital canal, is transmitted through a dis tinct canal, and escapes into the face through a separate forainen, situate internal to the infra orbital ; it ascends inward toward the lower lid, in front of the inferior margin of the orbit ; in its ascent it is situate beneath the orbicularis palpebrarnm, to which it gives filaments, which after supplying the muscle become cutaneous, and it is frequently contained in a superficial groove on the superior maxilla ; having reached the lid it divides into two branches, an external and an internal. The external runs outward, through the lid, toward the external angle, supplies its structures on that side, and anasto moses with filaments of the portio dura, and of the inferior palpebral branches of the lachrymal nerve. The internal ascends in the course of the original nerve toward the internal canthus of the eye, gives a filament to the side of the nose, which communicates with the naso-lobar branch of the nasal nerve, supplies the lower lid at its internal part, is also distributed to the carun cula and lachrymal sac, and anastomoses with a filament of the inferior branch of the infra trochlear nerve described in the account of that nerve. It sometimes anastomoses also with the portio dura.