The roots of the brachial plexus are the anterior rami of C5 to C8, and most of T1. Close to their origin, the roots receive gray rami communicantes from the sympathetic trunk (Fig. 7.52). These carry postganglionic sympathetic fibers onto the roots for distribution to the periphery. The roots and trunks enter the posterior triangle of the neck by passing between the anterior scalene and middle scalene muscles and lie superior and posterior to the subclavian artery.