Bilateral Chondroepitrochlearis Muscle: Incidence, Phylogenetic And Clinical Significance

IntroductIon The muscle mass of the pectoral region exhibits a variety of variations in the form of anomalous slips. The pectoralis major muscle is a thick triangular muscle that usually arises from the medial half of the clavicle, the sternum, and the first six costal cartilages. These three heads, the clavicular, the sternocostal and the abdominal, combine to form a tendon that inserts into the lateral lip of the bicipital groove of the humerus, after undergoing a twist. The pectoralis major muscle is innervated by the medial and the lateral pectoral nerves. The most common variations of the pectoralis major muscle include the absence of the abdominal slip, the decussation of the fibres across the midline and the absence of the sternocostal head [1], [2]. Mosconi and Ka-Math [3] have described a case in which the sternocostal head of the pectoralis major muscle was absent on the left and the entire pectoralis major muscle was absent on the right. Several cases of an additional musculature in the axillary region have also been reported. These include the following: a sternalis muscle which runs parallel to the sternum [4],[5] and a pectoralis quartus muscle which arises from the rectus sheath [6] runs parallel to the pectoralis major muscle and inserts into the tendon of the pectoralis major [1]