The length of the third division from the ganglion to its bifurcation is about three fourths of an inch, one fourth contained within the bone during its escape from the cranium, and the other two between the aperture externally and the division. When it divides into two, the branches are, at times, of the same size, but for the most part the inferior maxillary is the larger; they descend at first in close apposition with each other, but as they proceed they gradually separate, the lingual branch inclining inward and forward, the inferior maxillary outward, in the course of the original nerve, in order to gain the aperture of the dental canal ; they thus leave between them an angular interval, acute above, through which the internal maxillary artery for the most part passes. In their descent they cross, at right angles, the artery internal to the origin of the middle meningeal branch : in doing so either they pass both behind the vessel, or the lingual branch passes before, and the inferior maxillary behind it. The two nerves are most frequently connected, soon after their origin, by a short and delicate branch, which passes from the inferior maxillary to the lingual, and forms, with the nerves, a triangle, through which the artery passes in those instances in which the lingual descends before it.
The nerves are situate internal to the neck and ramus of the jaw, between the pterygoid muscles, posterior and inferior to the external, external and anterior to the internal ; and they are contained in a triangular space included between the two muscles and the jaw, bounded superiorly by the external, beneath and in ternally by the internal pterygoid, and externally by the jaw ; through this space they pass from above downward, the lingual from behind forward, and from without inward, the maxil lary from within outward, toward the aperture of the dental canal, and holding the mutual relation already indicated,—the lingual anterior and internal, the maxillary posterior and ex ternal.
Beforepursuing these branches of the third division further, it will he well to describe the superficial temporal nerve. This branch has been viewed differently by different autho rities; by some it is accounted one of the former set, the superior anterior branches of the third division ; by Mcekel it is described as one of three, into which the continuation of the nerve divides. It arises for the most part by two, and in some instances by three, roots ; a larger one from the inferior dental nerve, and a smaller from the trunk of the third division itself, given off at the same time with its superior branches, and deri ved from the same source ; the two roots forming together a loop, through which the middle meningeal artery ascends: in conse quence of this mode of origin it appears better to describe it thus separately, and not to refer it to either of the sets described. It has, however, been already explained that in some cases it appears to be an original branch of the third division, one of three into which it finally divides.
The nerve runs outward, backward, and somewhat upward, behind the external ptery goid muscle, toward the back of the neck of the lower jaw ; it then passes behind it and the condyle, between them and the auditory canal, traversing the posterior part of the glenoidal cavity of the temporal bone, and imbedded in the process of the parotid gland, which occupies it.
The superficial temporal nerve, while within the ramus of the jaw, pursues a course nearly the reverse of that of the trunk of the internal maxillary artery in the first part of its course. At first it is situate before the tensor palati muscle, between it and the external pterygoid ; then it passes between the internal lateral ligament of the maxillary articulation and the neck of the jaw, situate at the same time above and in contact with the artery ; and lastly, it is situate behind the condyle of the jaw, between it and the meatus auditorius, and involved in the parotid.
The nerve gives off numerous branches; when it has reached the situation last described, it breaks up at once into a leash of branches, which pass off in different directions : of these two, at times only one, are destined for the interior of the meatus auditorius ; they ascend toward the canal, become attached to its ex terior, and pass through the fibrous structure of the tube, close to its connection with the osseous portion : having thus gained its interior, they are distributed to its lining membrane, its sebaceous follicles, and the membrane of the tympanum. Before entering the tube they give some delicate filaments to its exterior ; these branches may be called the internal auricular.
Others, the smallest which the nerve gives off, descend along the external carotid artery, are in part distributed to the parotid gland, and establish upon the artery a manifest com munication with branches of the sympathetic. Its next branches, two in number, pass out ward through the substance of the parotid, behind the neck of the jaw ; one external or superficial, the other internal to the temporal artery; and turning forward round the posterior margin of the jaw, either they both, having given some fine ramifications to the gland, join the temporo-facial branch of the portio dun, immediately before its division, or one of them joins the facial branch of the tem poro-facial, while the other continues forward, upon the face, below the zygoma, and deeper than the branches of the temporo-facial : it divides into numerous long filaments, of which some join both branches of the temporo-facial ; others are distributed superficially upon the side of the face beneath the zygoma and upon the molar region, and, ascending over the former part, to the inferior anterior part of the temple, as far forward as the margin of the orbit. These may be called the commu nicating branches, in consequence of the re markable and important communication which they establish with the portio dura.