The axilla is a region of clinical and surgical importance with plenty of anatomical variations. One of these is the presence of accessory muscles. The literature was reviewed in order to identify the different supernumerary muscles that are described in the axilla. Variant muscle slips arising from the pectoral muscle or latissimus dorsi muscle have been described. There still remains controversy regarding the phylogenetic origin of these different muscles. We described the most frequently reported muscles, their origin, and course. Further research is required regarding the innervation and influence on glenohumeral and scapulothoracic kinematics.