The internal carotid artery is one of the two blood vessels that supply the brain with oxygenated blood; the other is the basilar artery. It arises from the common carotid artery at the level of the upper border of the thyroid as one of the two branches into which this artery divides, the other is the external carotid.
From its point of origin, the internal carotid artery runs upwards, medially and parallel to the jugular vein. Along its course to the base of the skull, the artery travels on the wall of pharynx medial to the parotid gland, from which it is separated by the stylohyoid and stylopharyngeous muscles. As it keeps ascending, it enters the carotid canal, following its bends, emerging through the foramen lacerum into the cavity of the skull.
The internal carotid artery usually gives off no branches in its cervical course. However, it sends the caroticotimpanic branch in the carotid canal of the petrous part of the temporal bone; this small artery supplies the mucous membrane of the tympanic cavity. Farther upwards, in the cavity of skull, the internal carotid gives off the ophthalmic artery, which supplies the eye and neighboring tissues.
Before it becomes the middle cerebral artery, the internal carotid gives off the anterior cerebral, the posterior communicating, which are part of the arterial circle of Willis, and the anterior choroid artery, which supplies the third ventricle, optic chiasm, internal capsule, globus pallidus, and hippocampus. Right at the base of brain, the internal carotid becomes the middle cerebral artery.
Below, schematic image of brain arteries, showing the internal carotid artery and its branches. The middle cerebral is the continuation of the internal carotid. (Side view).
Below, inferior surface of human brain. You can see the two main arteries that supply the brain; the basilar and the internal carotid.
