Very near the termination of the aqueduct of Fallopius, a minute twig connects the facial and vagus nerves. Following it from this cavity, it is seen to enter a small pore on its anterior surface, which conducts it by a short canal to the under surface of the petrous bone, where it emerges a very short distance in front of the stylo-mastoid foratnen, and be tween it and the jugular fossa. The nervous filament now turns inwards and forwards in front of the jugular vein, and terminates by connecting itself with the pneumogastric, just below its gang,lion in the dura mater of the foramen lacerum posticus.
Besides these branches of the facial within the aqueduct, it appears pretty constantly to give off', while yet contained in this canal, a filament which passes inwards behind the jugular vein, and joins with the glosso-pharyn geal just below the ganglion of Andersch. Longet states that this branch, after its junction with the glosso-pharyngeal, may ge nerally be traced to the digastric or sty lo-hyoid muscle, in which it often unites for the first time with this nerve by a kind of plexiform arrangement.
External to the cranium. —On leaving the Fallopian canal, the facial nerve immediately enters that portion of the parotid gland which dips downwards behind the styloid process to reach the structures lying deeply at the base of the skull. The nerve next continues through the substance of the gland, being, directed for wards and inwards to about its middle, where it divides into its temporo-facial and cervico facial portions, the ramifications of which cover the whole side of the face, with part of the neck below and the head above. In its short course previously to this bifurcation, it gives off' three branches, the posterior auri cular, the digastric, and the stylo-hyoid nerves.
The posterior auricular, the first branch of the facial without the skull, passes upwards from the trunk of the nerve, and turns round the front of the mastoid process, lying at first rather deeply in a depression between the au ricle of the ear and this prominence, and being enveloped in a dense cellular tissue. Having gained the side of the head, it divides into two branches ; one of these continues back wards in the horizontal direction, above the insertion of the sterno-rnastoid, and crossed by the lesser occipital nerve of the cervical plexus, to reach the posterior belly of the occipito frontalis muscle, which it supplies : in this course it is covered by a dense fitscia, and is in close proximity to the artery which bears the same name. The remaining branch of the
nerve takes a vertical direction, ascending perpendicularly behind the ear through the fleshy bundles of the retrahens aurem. To this muscle it is chiefly distributed ; but a few of its filaments continue to the posterior sur face of the auricle, probably to supply its transverse muscular fibres. The trunk of the posterior auricular nerve, or some one of these its branches, is usually found to be joined by filaments of the great auricular nerve from the cervical plexus, and more rarely by some twigs from the lesser occi pital branch of the same plexus. Arnold also describes a filament of the auricular of the pneumogastric uniting with it.
The two following branches not unfre quently arise by a common trunk. The di gastric, the larger of the two, leaves the facial nerve to penetrate the posterior belly of the digastric muscle, and supply it with many filaments. One of its branches, of more con siderable magnitude, perforates its substance, and passing directly inwards, joins the glosso pharyngeal immediately on its emergence from the skull. Other filaments of smaller size are said to join the superior laryngeal of the pneu mogastric.
The stylo-hyoid branch, leaving the trunk of the portio dura near the preceding, plisses downwards, forwards, and inwards ; crossing the styloid process obliquely, then running along the upper border of the muscle, and finally penetrating its fibres to be distributed to its interior. It is believed to unite, by nu merous minute twigs, with the sympathetic around the neighbouring carotid vessels.
At the place of its &vision, the nerve occu pies a position in the parotid gland which is superficial to the many other vessels and nerves found here ; and especially, at right angles to the external jugular vein and carotid artery.
The tenzporo-facial division or branch is larger than the cervico-facial ; it passes forwards and upwards over the condyle of the lower jaw, and joins, towards the zygoma, with one or two large branches of the auriculo-temporal nerve. This comes from the third division of the fifth in the pterygoid fossa ; and the place of its union with the portio dura is in close proximity to the external carotid artery. The intimacy of the junction which connects the two nerves has probably led some anatomists to describe this temporo-facial branch as giving many filaments to the front of the ear. These, however, with many others which ramify in the gland itself, belong to the associated branch of the fifth, and not to the portio dura.