Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content ++ Two independent layers from the roots to terminal branches: A simple and constant dorsal layer: extensor and supinator musclesA complex and variable ventral layer: flexor and pronator muscles: This explains the variations and the relationships between the median, musculocutaneous, and ulnar nervesThe brachial plexus can be: “Prefixed” with a contribution from C4 (two thirds of cases), orNormal, or“Postfixed,” with the participation of T2Or even spread in both directions: Clinical significance of these variations because motor and sensory distributions are modifiedOrigin of the trunks: Upper trunk: confluence of the ventral branches of C5 and C6 (C4 participation, prefixed plexus)Middle trunk: ventral division of C7Lower trunk: confluence of the ventral branches of C8 and T1Constitution of the cords (most common configuration): Lateral cord: confluence of ventral divisions of upper and middle trunks (80% of cases)Medial cord: ventral division of lower trunk (95% of cases)Posterior cord: confluence of dorsal divisions of the three trunks (70% of cases)Constitution of terminal nerves = branches (at distal edge of the pectoralis minor muscle): Posterior cord: posterior plane of the brachial plexus, with mainly radial and axillary nervesLateral and medial cords: anterior plane of the brachial plexus with mainly the median nerve, as well as musculocutaneous and ulnar nerves ++Figure 131-1. Brachial PlexusGraphic Jump LocationView Full Size||Download Slide (.ppt)++Figure 131-2. Brachial Plexus and Muscle InnervationGraphic Jump LocationView Full Size||Download Slide (.ppt) Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth