A Rare Anomaly of the Pectoralis Major ? the Chondroepitrochlearis

The chondroepitrochlearis was found in the left upper extremity of a 92-year-old Japanese male.This represents the second report of the anomaly in Japan after Yokoh ('33).The pars abdominalis of the pectoralis major consisted of two slender muscle slips, A and B, and after arising from the lower costal cartilages as normal, they took a somewhat horizontal course towards the axilla, being separated from the parent muscle.Slip A was attached to the aponeurotic sheet deep to the insertion of the pectoralis major and abruptly turned its course downwards along the humerus.It then continued to the characteristic long slender tendon and finally inserted onto the medial epicondyle of the humerus.Slip B passed caudal to slip A, and in the axilla it crossed the muscular arch which arose from the latissimus dorsi.The most caudal pectoral nerve arising from the ansa pectoralis supplied both the muscle slips together with the muscular arch of the axilla.According to Saar ('03), the insertion of the pectoral muscles in ungulates sometimes migrates distalwards along the humerus and is onto the medial epicondyle of the humerus.The aberrant muscle under discussion here would thus be a phylogenetic recapitulation of this condition.Tobler ('02) and Ruge ('14) have also suggested that the chondroepitrochlearis in man would be derived from the panniculus carnosus of lower mammals, and this was demonstrated by the present authors from the nerve supply.Crossing of the separated abdominal part of the pectoralis major with the muscular arch of the axilla was a noticeable finding of the anomaly, and the authors consider that it would be closely related genetically with the appearance of this anomaly.