The external carotid artery (carotis superficialis s. externa, — Haller), is smaller than the internal carotid in young subjects, but about of equal size in the adult. It reaches in the neck from the point of division of the common carotid (opposite the upper margin of the thyroid cartilage) to the neck of the condyle of the lower jaw-bone, or a little lower, where it divides into two branches, the temporal and the internal maxillary. This artery diminishes rapidly in size as it ascends in the neck, owing to the number and size of the branches which spring from it.
At first the external carotid lies to the inner side, i. e. nearer to the middle line of the body, than the internal carotid, — the distinctive names of the two arteries having reference to their destination to parts nearer or more remote from the surface. Soon after its origin the external carotid crosses over or becomes superficial to the internal carotid, and then curves slightly forward as it ascends to its place of division. For a short distance after its origin this artery is covered only by the platysma muscle, and the fascia, and is placed in the triangular intermuscular space, bounded by the sterno-mastoid, omo-hyoid and digastric muscles; but it soon becomes deeply placed passing beneath the stylo-hyoid and digastric muscles, and finally becomes embedded in the substance of the parotid gland.' On its inner side it is close to the hyoid bone, and afterwards to the back part of the ramus of the lower maxilla, a portion of the parotid gland being interposed between the bone and the artery. It is close to the pharynx for a short space, and afterwards rests upon the stylo-glossus and stylo-pharyngeus muscles, which, with the glosso-pharyngeal nerve, are interposed between it and the internal carotid artery.
Two small veins accompany the external carotid artery, and it is crossed by superficial venous branches belonging to the external jugular, and other veins.
Near its commencement the external carotid is crossed by the hypoglossal nerve, and at a short distance from its upper end, in the substance of the parotid gland, by the portio dura of the seventh. The glosso-pharyngeal nerve, as already mentioned, lies between this artery and the internal carotid, and the superior laryngeal nerve is under both vessels.
Peculiarities of the external carotid artery
The variations in the place of origin, and consequently in the length of the external carotid artery, are determined by the point of division of the common carotid, which has been already described. In the same place will be found reference to examples of the external carotid taking rise from the arch of the aorta.