4. The fifth and last of these branches is the pterygoid; it is the smallest of them, and arises from the anterior internal part of the trunk ; it passes inward and downward, be hind the external pterygoid, and then between the internal pterygoid and eireumflexus palati muscles; it gives a filament of some size to the latter muscle, and then entering into the internal pterygoid at its upper extremity, it is consumed altogether in that muscle.
The external pterygoid also, at times, but not uniformly, receives a distinct filament from the trunk; when present it arises from the front of the nerve, beneath the buccal branch, and passes forward directly to the muscle, in which it is consumed. The constitution of these branches is peculiar, and is a matter of much interest: involving physiological ques tions, this subject is deferred to another oc casion.
In consequence of its connection with the third division of the fifth, and more particularly with the lesser packet of the nerve, this seems a fit place to advert to the ganglion discovered by Arnold, and by him denominated Otic or auricular, of which the following sketch has been taken from his own account. It is situate at the inner side of the third branch of the fifth, some lines beneath the foramen ovale, at the part where the deep temporal, the masseterio, and the buccal nerves are de tached from the same side, and a little above the origin of the superficial temporal nerve : its posterior part touches the middle ineningeal artery, and the internal the internal pterygoid muscle : an abundant adipose tissue surrounds it : its form is not altogether regular, however it approaches to an oval, flattened internally and externally. It is united to the trunk of the third division not merely by cellular tissue, but by many filaments, which enter into the formation of the ganglion ; these filaments, which come solely from the lesser portion of the nerve, are mostly extremely short, and can only be observed when we try to separate the ganglion from the trunk ; but in eases where the ganglion is situate rather distant from the nerve, the filaments are of course longer and can be more easily observed. With regard to the branches of the third division, the pterygoid nerve espe cially is in very intimate connection with the otie ganglion, so that in a superficial examina tion it appears as if it arose from it ; but, in a more accurate investigation, it is clear that this nerve soon after its origin penetrates through a part of the substance of the ganglion and takes up some of it : the slender branch, which ramifies in the tensor palati, is likewise in very intimate relation with this ganglion, and distinguishes itself from the other branches by its reddish appearance. The ganglion thus
communicates with the lesser packet of the fifth : it also communicates with the glosso pharyngeal and with the facial and auditory nerves by means of the nervus tympanicus. But, the ganglion being a body which is to be regarded as distinct from the fifth nerve, and not part of it, a further pursuit of its connections and properties would he here out of place. See SYMPATHETIC NERVE.
The third division of the fifth descends from the foramen ovale, outward into the zygomatic fossa, posterior to the external pterygoid muscle, before the superior part of the levator palati, and internal and parallel to the middle me ningeal artery. After a course of half an inch from the foramen, it divides for the most part into two large branches, an anterior internal one destined to the tongue, denominated the lingual branch, and an external posterior one, which is transmitted through the inferior max illary canal, and, escaping from this, through the mental foramen, is distributed finally to the muscles and integuments of the chin ; this second branch is called inferior dental, or inferior maxillary nerve ; the latter, as has been already intimated, appears much the more appropriate appellation.
The first branch bears, very generally, the name of gustatory nerve from its presumed connection with the sense of taste; but, since the opinion that it is the nerve in which the sense of taste resides has been brought into question, and since, as will appear by-and bye, it is at least certainly not the sole nerve of that sense, it is obvious that that name should be discontinued.
The manner in which the third division finally divides is not always such as has been described : in some instances it separates fairly into three branches, viz. the lingual, the inferior maxillary, and the superficial temporal, and such is the mode of division mentioned by the elder Meckel. The writer has before him an instance of another mode ; the inferior maxillary arises by two roots, and the original trunk divides into two parts ; one common to the lingual, and one root of the maxillary; the other to the superficial temporal and the other root: the superficial temporal is thus, in this instance, equally an original branch as the others, and is connected to the maxillary by a filament, which it gives off soon after its origin, while the maxillary is also connected in the usual mode to the lingual : the maxillary artery, however, passes through the loop formed by the two roots of the former nerve.