Magendie* states himself to have succeeded, in one instance, in exposing the facial nerve within the skull, or where it enters the auditory meatus ; and adds that it was in sensible to irritation. But the experiment stands alone, and it appears doubtful whether the portio interrnedia was included in the irritation.
But the anatomical discoveries of Morganti may somewhat supply the deficiency of direct evidence. He has pointed out the complete analogy of the facial to a spinal nerve and hence deduces the probability, that the portio intermedia, which exclusively forms the geni culate ganglion, is, like the posterior or gan gliform root of the spinal nerve, the source of sensitive fibres to the compound nerve.
The observed insensibility of the facial after section of the fifth militates strongly against this view. But it will be recollected that although affirmed by some, it has been denied by others. And even granting it to be as complete as Longet states it, yet possibly it would constitute a less conclusive objection than might at first appear. For when we consider the violent nervous shock which division of the important trifacial must pro duce on the parts in the immediate neigh bourhood of its origin, and the close prox imity of the two nerves at their roots, we are perhaps justified in considering the result an insufficient testimony to their more imme diate connection. A comparison of the lesion and symptoms in many cases of cerebral hemorrhage would almost parallel the occur rences of such an anwsthesia; while, in such an instance, a direct continuity would scarcely be admitted.
But even granting that the facial nerve, as thus constitu.ted, possesses an inherent sensibility, it is still probable, from its nu merous anastomoses, both with the fifth and with the cervical nerves, that it subsequently receives many additional sensory filaments. These junctions differ from a plexus like the cervical, or brachial, in the fact that. in place
of forming communications between the mixed nerves of different segments of the body, they connect nerves of different endowments. The exchange appears to be at the expense of the sensitive nerve ; that is, more filaments seem to pass from the fifth to the facial than from the latter to the former. The amount of these filaments given to the different branches of the seventh is said to differ : thus, Longet affirms the insensibility of the " mentonnier," or supra-maxillary portion.
Little can here be said of the more minute ramifications of Morganti's theory.* But nothing that is known at present, either of the facial generally, or of the chorda tympani, or superficial petrosal branches, is absolutely incompatible with his views. All of these branches, except the lesser petrosal, he shows to be mixed nerves : the experiments and observations above quoted tend to indi cate all as more or less directly subservient to motion ; and in none are we able to deny the possibility of sensation. But the petrosal nerves would probably be likened to the branches which connect the roots of the spinal nerves to the sympathetic ganglia on the side of the spine ; and the obscure and un certain results obtained by experiment on these filaments of the facial are closely analogous to the effects of sirnilar experiments on the spinal nerves in connection with the sympathetic of the trunk. But the anomaly of the tensor tympani being apparently supplied solely from the sensitive portion of the facial nerve, is very much weakened by the physiological facts of the involuntary character of its movements, and the interposition of a second ganglion.
The more important effects of disease of the facial nerve have already been spoken of in treating of its functions. For its morbid anatomy, in which it offers no especial pecu liarity, reference is made to the article