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7a. The Cephalic Portion of the Sympathetic System
(Pars Cephalica S. Sympathici)
The cephalic portion of the sympathetic system begins as the internal carotid nerve, which appears to be a direct prolongation of the superior cervical ganglion. It is soft in texture, and of a reddish color. It ascends by the side of the internal carotid artery, and, entering the carotid canal in the temporal bone, divides into two branches, which lie one on the lateral and the other on the medial side of that vessel.The lateral branch, the larger of the two, distributes filaments to the internal carotid artery, and forms the internal carotid plexus. The medial branch also distributes filaments to the internal carotid artery, and, continuing onward, forms the cavernous plexus. The internal carotid plexus (plexus caroticus internus; carotid plexus) is situated on the lateral side of the internal carotid artery, and in the plexus there occasionally exists a small gangliform swelling, the carotid ganglion, on the under surface of the artery. The internal carotid plexus communicates with the semilunar ganglion, the abducent nerve, and the sphenopalatine ganglion; it distributes filaments to the wall of the carotid artery, and also communicates with the tympanic branch of the glossopharyngeal nerve. The communicating branches with the abducent nerve consist of one or two filaments which join that nerve as it lies upon the lateral side of the internal carotid artery. The communication with the sphenopalatine ganglion is effected by a branch, the deep petrosal, given off from the plexus on the lateral side of the artery; this branch passes through the cartilage filling up the foramen lacerum, and joins the greater superficial petrosal to form the nerve of the pterygoid canal (Vidian nerve), which passes through the pterygoid canal to the sphenopalatine ganglion. The communication with the tympanic branch of the glossopharyngeal nerve is effected by the caroticotympanic, which may consist of two or three delicate filaments. The cavernous plexus (plexus cavernosus) is situated below and medial to that part of the internal carotid artery which is placed by the side of the sella turcica in the cavernous sinus, and is formed chiefly by the medial division of the internal carotid nerve. It communicates with the oculomotor, the trochlear, the ophthalmic and the abducent nerves, and with the ciliary ganglion, and distributes filaments to the wall of the internal carotid artery. The branch of communication with the oculomotor nerve joins that nerve at its point of division; the branch to the trochlear nerve joins it as it lies on the lateral wall of the cavernous sinus; other filaments are connected with the under surface of the ophthalmic nerve; and a second filament joins the abducent nerve. The filaments of connection with the ciliary ganglion arise from the anterior part of the cavernous plexus and enter the orbit through the superior orbital fissure; they may join the nasociliary branch of the ophthalmic nerve, or be continued forward as a separate branch. The terminal filaments from the internal carotid and cavernous plexuses are prolonged as plexuses around the anterior and middle cerebral arteries and the ophthalmic artery; along the former vessels, they may be traced to the pia mater; along the latter, into the orbit, where they accompany each of the branches of the vessel. The filaments prolonged on to the anterior communicating artery connect the sympathetic nerves of the right and left sides.
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