Little can be said with respect to the exact nature of these very numerous junctions of the facial nerve, either with the terminal branches of the various divisions of the fifth, or with the cutaneous nerves of the cervical plexus. They offer a very, obvious anatomical resemblance to that intermingling of different nerves which constitutes a plexus ; but with out here specifying other distinctions, it may suffice to point out that, in many instances, the branches of the facial seem visibly con tinued in their previous direction beyond their connections with the fifth. In the absence of more minute investigations, this apparent in dependence can only be received as indicating a partial involvement of the two nerves, or an incomplete mixture of their fibres, in which one gives to the other, or each gives to each, a small number of its filaments, but retains the large majority.
We next proceed to consider those rninuter features in the anatomy of the seventh nerve, which require a more artificial dissection or examination for their verification.
The origin of the portio intermedia, rather more externally than the facial, has been al ready spoken of, and the nerve was then traced to an union, more or less complete, with the neighbouring vestibular portion of the auditory nerve. Beyond this point the views adopted respecting it, from being some what conflicting, become absolutely discor dant.
The very different nature of the numerous opinions upheld by various anatomists pre cludes the possibility of enumerating them here at full length. Some of these, however, have been already very briefly noticed ; and perhaps, on the whole, the most prevalent was that which supposed the portio intermedia to give a branch which united with the vestibular nerve, while the remaining portion passed itself into the facial.
More recently, the anatomy of the distribu tion and connections of this nerve seems to have been fully made out by Morganti in an elaborate monograph on the Geniculate gang lion* ; which is, I believe, chiefly known in this country through the medium of an ex cellent analysis contained in one of Mr. Paget's Reports.t By careful dissection of the nerves, which he had previously hardened in nitric acid, Morganti' succeeded in unravelling their filaments ; and thus in separating the portio intermedia from the facial and vestibular nerves to a much greater extent than had hitherto been accomplished. The general result of this process was, that many of the so-called anastomoses were shown to be mere relations of propinquity, due to an intricate entangle ment, but not implying any real junction or interchange of fibres.
In the human subject,— The portio inter media Cfig. 405, b), shortly after its origin, and while lying closely by the side of the vestibular branch of the auditory nerve (c), gives off' a filament (d), which passes towards it. Before joining with it, however, a similarly small branch which comes off from the latter nerve, unites with that previously given from the portio intermedia, and the common trunk thus formed passes into and is lost in the vestibular nerve.
The intermediate nerve next emits two small filaments (e), which join the portio dura, and cannot be satisfactorily traced through its trunk.
The description is now complicated by the introduction of a large branch of the facial (f) which emerges from it to take a spiral course around the portio intermedia ; and which, after running with it for some distance, re turns to the facial at a lower point than that from which it set out.
Setting aside this fictitious junction, the whole of the portio intermedia, after the giving off of the facial and auditory branches, was traced into the genuform intumescence : this, it will be recollected, is seated on the , first bend of the facial in the Fallopian canal, and close to the hiatus of the same name.
The nature of this intumescence is the next question to which the description directs itself, and is perhaps even more important than the precedimr dissections. The appear ances of this swe'lling, and its reddish-grey colour, had long given rise to conjectures of its ganglionic nature. Many anatomists, in deed, have affirmed its identity with the true ganglions. By others, however, it has been somewhat obscurely described as intermediate in structure between a ganglion and a gangli form enlargement: a description vvhich can only be understood as indicating their doubt of its ganglionic character, since the supposi tion of such a gradation of texture is perfectly gratuitous. And others have altogether de nied its ganglionic characters ; attributing its colour to the minute vessels which pass through the hiatus Fallopii to the facial nerve and internal ear, and explaining the appearance of enlargement or intumescence by the diver gence of the fibres of the superficial petrosal nerve where it joins the facial.