Internal carotid plexus

The internal 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.

Internal carotid plexus
Sympathetic connections of the ciliary and superior cervical ganglia. (Carotid plexus visible center top.) Note that the label "Sympathetic Efferent Fibres" above the nerves arising in the midbrain is an error. This label should read "Parasympathetic Efferent Fibres" as the sphincter pupillæ and ciliary muscle are innervated only by parasympathetic fibres.
Diagram of the cervical sympathetic. (Carotid plexus visible center top.)
Details
Identifiers
Latin	Plexus caroticus internus
TA98	A14.3.03.004
TA2	6645
FMA	67533
Anatomical terms of neuroanatomy

Scheme showing sympathetic and parasympathetic innervation of the pupil and sites of lesion in a Horner's syndrome.

Postganglionic sympathetic fibres ascend from the superior cervical ganglion, along the walls of the internal carotid artery, to enter the internal carotid plexus. These fibres then distribute to deep structures, which include the Superior Tarsal Muscle and pupillary dilator muscles.[1] Some of the fibres from the internal carotid plexus converge to form the deep petrosal nerve.[2]

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.