It is composed of post-ganglionic sympathetic fibres which have synapsed at (i.e. have their nerve cell bodies at) the superior cervical ganglion.

[3] Some fibres of the plexus converge to form the deep petrosal nerve.

[4] The internal carotid plexus communicates with the trigeminal ganglion, the abducent nerve, and the pterygopalatine ganglion (also named sphenopalatine); it distributes filaments to the wall of the internal carotid artery, and also communicates with the tympanic branch of the glossopharyngeal nerve.

[citation needed] The plexus there occasionally presents a small gangliform swelling - the carotid ganglion - on the under surface of the artery.

[citation needed] This article incorporates text in the public domain from page 977 of the 20th edition of Gray's Anatomy (1918)