A new variety of chondrocoracoideus muscle, or an additional head of pectoralis major muscle

Abstract

The pectoralis major and pectoralis minor muscles are located in the anterior chest wall. This region is characterized by high morphological variability. During dissection an additional muscle was found, originating from the lateral border of the pectoralis major muscle. After fusion it passed into the tendinous part coursing under the insertion of the pectoralis major muscle, then formed a common junction with the short head of the biceps brachii muscle, the distal attachment of which is on the coracoid process. Such an accessory structure could lead to neurovascular compression and cause thoracic outlet syndrome, of which pain is usually the first symptom. This muscle has not been described in the literature so far and for that reason we can name the present case as an unique structure.

Keywords: Accessory muscle; Chondrocoracoideus; Morphological variation; Pectoralis major muscle; Pectoralis minor muscle; Thoracic outlet syndrome.

Fig. 1

Anterior view of the rare case of the pectoralis major muscle. C clavicle, cPM clavicular part of the pectoralis major muscle, sPM sterno-costal part of the pectoralis major muscle, aPM abdominal part of the pectoralis major muscle, CP coracoid process, shBB short head of the biceps brachii muscle. lhBB long head of the biceps brachii muscle, the white stars indicates the accessory part of the pectoralis major muscle

Fig. 2

Posterior view of the rare case of the pectoralis major muscle. C clavicle, cPM clavicular part of the pectoralis major muscle, sPM sterno-costal part of the pectoralis major muscle, aPM abdominal part of the pectoralis major muscle, CP coracoid process, shBB short head of the biceps brachii muscle, the white stars indicates the accessory part of the pectoralis major muscle