Page 205 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 190

190 The upper limb

•◊◊a medial, from the anterior division of the lower trunk;
•◊◊a posterior, from the union of all three posterior divisions.
The roots lie between the anterior and middle scalene muscles. The
trunks traverse the posterior triangle of the neck. The divisions lie behind the
clavicle. The cords lie in the axilla.
The cords continue distally to form the main nerve trunks of the upper
limb thus:
1◊◊the lateral cord continues as the musculocutaneous nerve;
2◊◊the medial cord, as the ulnar nerve;
3◊◊the posterior cord, as the radial nerve and the axillary nerve;
4◊◊a cross-communication between the lateral and medial cords forms the
median nerve.
For reference purposes, the derivatives of the various components of
the brachial plexus are given below (Fig. 139).
From the roots
•◊◊nerve to rhomboids;
•◊◊nerve to subclavius;
•◊◊nerve to serratus anterior (C5, 6, 7).

Fig. 139◊The derivatives of the brachial plexus. The lightly coloured areas show the
posterior divisions.