Although only part of the brachial plexus is found in the
axilla, we will present a general layout of the plexus before
covering the parts that are found in the axilla. Whoever first
described the brachial plexus must have been a nature lover, or
at least a tree lover, because the various parts of the plexus
are named according to various parts of a tree, starting from
the roots. |The brachial plexus starts in the neck from the
ventral rami of spinal nerves C5 - T1 (5th cervical to 1st
thoracic spinal cord segments). These rami are called roots. The
roots will continue through the neck and, some of them merge, to
form trunks. C5 and C6 form the upper trunk, C7 continues as the
middle trunk and C8 and T1 for the lower trunk. While still in
the neck, the trunks divide into anterior and posterior
divisions. The divisions then reunite in different patterns. The
anterior divisions of the upper and middle trunks merge to form
the lateral cord. The anterior division of the lower trunk
continues as the medial cord. T