The axillopectoral muscle, usually called Langer's axillary arch instead of Langer's arm arch, is a supernumerary muscle and is the principal anatomic variation of the axilla. Three cases of the muscle were observed originating from latissimus dorsi crossing over the axillary neurovascular bundle and inserting deep to the insertion of pectoralis major or into the coracoid process. Clinicians should be aware of its existence as it can give rise to different pathologies. It should be recognised and excised to expose the axillary artery and vein in patients with trauma and to perform axillary lymphadenectomy or axillary bypass. It should be considered in the differential diagnosis of axillary masses or in a history of intermittent axillary vein obstruction. If the muscle causes problems its excision should be curative.