The sternocleidomastoid branches of the occipital artery usually arise as an inferior and superior branch.  The inferior branch originates near the origin of the occipital artery, sometimes from the external carotid artery itself, whereas the superior branch arises as the occipital artery crosses the accessory nerve (XI cranial nerve).  The inferior branch descends postero-laterally over the internal jugular vein and the hypoglossal nerve (XII cranial nerve), to pierce the sternocleidomastoid muscle and anastomose with the sternocleidomastoid branch of the superior thyroid artery.  In contrast, the superior branch descends sharply lateral to the internal jugular vein and enters the deep layers of the sternocleidomastoid with the accessory nerve (XI cranial nerve).