Bilateral axillary arch muscle with absence of posterior cord of brachial plexus

Axillary arch is an additional muscle slip usually joining the latissimus dorsi muscle to the pectoralis major or other neighboring muscles and bones. In this paper, rare case of bilateral axillary arch muscle is reported during routine dissection of the axillary region of 60-year-old male cadaver with absence of posterior cord formation of brachial plexus.
On both sides, the axillary arch muscle took origin from fascia covering latissimus dorsi muscle and passed upwards between dorsal divisions of middle and lower trunk anteriorly, and dorsal division of upper trunk posteriorly; but posterior to the bulk of axillary neurovascular bundle. Then it split into two slips, medial slip was inserted into coracoclavicular ligament and lateral slip was inserted into coracobrachialis muscle.
The presence of the arch muscle has important clinical implications and the bilateral presence, absence of posterior cord formation and multiple connective tissue attachments makes the case most unique.