Petrous portion of the internal carotid artery (or petrous segment).—When the internal carotid artery enters the canal in the petrous portion of the temporal bone, it first ascends a short distance, then curves forward and medially, and again ascends as it leaves the canal to enter the cavity of the skull between the lingula and petrosal process of the sphenoid.
The artery lies at first in front of the cochlea and tympanic cavity; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age.
Farther forward it is separated from the semilunar ganglion by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal.
Frequently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane.
The artery is separated from the bony wall of the carotid canal by a prolongation of dura mater, and is surrounded by a number of small veins and by filaments of the carotid plexus, derived from the ascending branch of the superior cervical ganglion of the sympathetic trunk.
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