Figure 11. The brachial plexus may be divided into roots, trunks, divisions and cords. The upper trunk is formed from the union of the roots C5 and C6, the middle trunk is a continuation of C7 root and the lower trunk is formed by the union of C8 and T1 roots. Each trunk divides into anterior and posterior divisions. The lateral cord is formed by the union of the anterior divisions of the upper and middle trunks. The medial cord is formed by the anterior divisions of the lower trunk. The posterior cord is formed by the union of the posterior divisions of all the trunks.