The right common carotid artery originates from the innominate (brachiocephalic) artery. The external landmark is the right sternoclavicular joint. The left common carotid artery originates directly from the aortic arch in the superior mediastinum.
The carotid sheath contains the common and internal carotid arteries, the internal jugular vein, and the vagus nerve. The internal jugular vein lies lateral and superficial to the common carotid artery and vagus nerve. The vagus nerve lies posteriorly, between the artery and the vein. On occasion the vagus nerve may be located anterior to the vessels.
The carotid sheath and its contents are covered superficially by the platysma, anterior margin of the sternocleidomastoid muscle, and the omohyoid muscle. Deep to the vessels are the longus colli and longus capitis muscles. Medial to the carotid sheath is the esophagus and trachea.
At the level of the superior border of the thyroid cartilage, the common carotid artery bifurcates into the internal and external carotid arteries.
The facial vein crosses the carotid sheath superficially to enter the internal jugular vein at the level of the carotid bifurcation.
The external carotid artery lies medial to the internal carotid artery for the majority of their course. The first branch of the external carotid artery is the superior thyroid artery located near the carotid bifurcation.
The internal carotid artery does not have any extracranial branches.
At the level of the angle of the mandible, the internal and external carotid arteries are crossed superficially by the hypoglossal nerve (Cranial Nerve XII) and the posterior belly of the digastric muscle. The glossopharyngeal nerve (Cranial Nerve IX) passes in front of the internal carotid artery, above the hypoglossal nerve.
The external carotid arteries terminate in the parotid gland, where they divide into the superficial temporal and maxillary arteries.
At the level of the skull base, the internal carotid arteries cross deep and medial to the external carotid arteries to enter the carotid canal behind the styloid process.
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