Figure 2. Anomalies in the proximal part of the brachial plexus. (A) Image of the roots and trunks of the anomalous plexus showing the C4 and C5 roots emerging anterior to the anterior scalene muscle and joining to form the superior trunk (ST). The anterior rami of nerve roots C6 and C7 emerged between the anterior and middle scalene and continued laterally to form the superior middle and inferior middle trunks (SMT and IMT, respectively). Nerve roots C8 and T1 joined to form the inferior trunk (IT). (B) A high-magnification image of the distal portion of the trunks and divisions re-joining to form cords. Blue lines indicate contributions to the anterior divisions and red lines indicate contributions to the posterior divisions. Hidden portions of the divisions are indicated by dashed red and blue lines. Cadaveric orientation and viewing angle are by cardinal arrows the red dashed line in the lower right corner, respectively.