PLEXUSES OF THE SYMPATHETIC.
A. In the Head.—The chief plexuses of the sympathetic which exist in the head are the internal carotid plexus, cavernous, and external carotid. There are also present in different parts of the head several ganglia : the principal of these are the ciliary ganglion, spheno-palatine, otic, and submaxillary. These ganglia have been already described in this work in the articles on the different nerves with whose branches they are connected.
1. Internal Carotid Plexus.— The internal carotid plexus is formed by the ascending branches of the superior cervical ganglion, and surrounds the internal carotid artery during its passage through the carotid canal. The as cending branch of the superior cervical gan glion, as was already stated, divides into two portions, one of which passes along the outer and anterior aspect of the artery, while the other lies on the inner and posterior aspect of the same vessel. The external portion is chiefly concerned in the formation of the carotid plexps, the inner in forming the cavernous plexus. The carotid plexus is thus situated chiefly on the outer side of the artery between its second and third bends. The branches connected with the plexus are,— (a) Two or three filaments of communica tion with the sixth pair of nerves; they join the nerve as it passes along the cavernous sinus. One of these, stronger than the others, was formerly regarded as one of the roots of the sympathetic nerve. One filament is said sometimes to run only a short distance with the sixth nerve, when it leaves it and passes to the ciliary ganglion, or to the spheno-pala tine.
(b) Great or deep Petrosal Nerve.—This branch, commonly- termed the deep branch of the Vidian nerve, may be regarded as passing front the fifth pair to the sympathetic, or vice versa. Regarding it as the latter, it may be described as passing out by the superior ori fice of the carotid canal, traversing the car tilaginous substance which occupies the an terior lacerated foramen to reach the pterygoid canal, where it becomes associated with the cranial division of the Vidian, along with which it traverses the canal from behind for wards, and terminates in the ganglion of Meckel. In the interior of the pterygoid
canal, the two nerves are merely placed side by side wi.th each other, and after leaving the canal are connected separately with the gan glion. The greater or deep petrosal nerve was formerly regarded as the second of the two roots by which the sympathetic was sup posed to begin.
(c) From three to five delicate ;short branches pass through the outer wall of the cavernous sinus and join the Gasserian ganglion on its inner surface. One or two of these have been described as passing backwards to the ten torium cerebelli, and have been traced by Arnold to the walls of the transverse sinus. The filaments to the Gasserian ganglion are sometimes supplied by the cavernous plexus.
2. Cavernous Plexus.— This name is applied to the plexus formed around the internal carotid artery as it lies in the cavernous sinus; it is situated rather towards the inner surface of the vessel, at the point where it makes its highest turn.
The branches which leave the cavernous plexus are the following: — (a) Filaments which join the third nerve; they are two or three in nutnber, and become united with the nerve before its entrance into the orbit. Hirzel regards the communication as rare, having found it only in ten bodies ; in some cases he found that the supposed nerve filaments con sisted merely of cellular tissue. Bock, Longet, and others regard it as constant. (b) Branches of communication to the fourth nerve ; they are either derived from the cavernous plexus or from the carotid, and join the nerve as it lies in the cavernous sinus. (c) Communi cating filaments with the ophthalmic ganglion, one or two in number, emerge from the an terior part of the cavernous plexus, and enter the orbit on the inner side of the ophthalmic division of the fifth nerve, either ending di rectly in the posterior border of the ophthalmic ganglion, or joining the long root derived from the nasal branch of the ophthalmic. Occa sionally one filament enters the posterior bor der of the ganglion, the other along with the long root derived from the nasal branch.