The course and relations of the hypoglossal nerve and the occipital artery.

Three main types of variations in the relations of the occipital artery and the hypoglossal nerve found in 42 dissected specimens are described, according to the level at which the nerve crosses the external carotid artery and the point of origin of the occipital artery. In Type I, the hypoglossal nerve crosses the external carotid artery inferior to the origin of the occipital artery; in Type II, the nerve crosses the external carotid artery at the level of origin of the occipital artery; and in Type III, it crosses superior to that level. In Type III the occipital artery makes a loop around the hypoglossal nerve and is in a position to pull and exert pressure on the nerve. This possibility should be taken into consideration in the diagnosis of peripheral paresis or paralysis of the tongue and during surgery in this area.