Extracranial lateral face and neck dissection. The right common carotid artery (transected from the brachiocephalic trunk) ascends within the carotid sheath medial to the internal jugular vein (IJV). Between these two vessels is the vagus nerve.  At about the upper border of the thyroid cartilage of the larynx the common carotid bifurcates into the external and internal carotid arteries. The latter gives off no branches in the neck. Deep to the internal jugular vein is the anterior scalene muscle, which with the middle scalene and first rib form the interscalene triangle through which descends the roots and trunks of the brachial plexus as well as the subclavian artery. Descending through the posterior triangle of the neck is the spinal accessory nerve that provides motor innervation to the sternocleidomastoid and trapezius muscles. The thyroid gland receives blood from two sources: the superior thyroid artery (a branch of the external carotid) and the inferior thyroid artery (a branch of the thyrocervical trunk). It is drained by three pairs of veins; the superior and middle thyroid veins to the IJV, and the inferior thyroid vein to the brachiocephalic vein. The deep chain of cervical lymph nodes are organized along the IJV. A named node of this group is the jugulodigastric node located near the intersection of the IJV with the posterior digastric muscle. The hypoglossal nerve is shown descending in the neck, but near the tip of the greater horn of the hyoid bone takes a more horizontal course toward the floor of the mouth to supply most of the musculature of the tongue. Where it changes direction, the superior root of the ansa cervicalis (consisting of C1 nerve fibers) leaves the epineurial covering of the hypoglossal nerve to descend in the neck. This root unites with the inferior root (containing fibers from C2, C3) of the ansa, which usually wraps around the lateral surface of IJV. Branches of the ansa cervicalis supply motor innervation to the infrahyoid muscles. (Image courtesy of AL Rhoton, Jr.)