Thoracic Wall Muscles

Many of the supernumerary muscles of the anterior thoracic wall region may be traced back to the abnormal development of the pectoral muscle mass. The pectoralis major muscle develops from the ventral sheet of the pectoral mass and grows onto the thorax. The pectoralis minor muscle is said to attach to the coracoid process superiorly and ribs three-five inferiorly. Poland's syndrome is a rare congenital anomaly characterized by a hypoplasia of the chest wall and associated thoracic wall musculatures, neurovascular abnormalities, and hypoplasia of the musculature of the ipsilateral upper limb. The pectoralis tertius is derived from the entopectoral muscle sheet; it is usually absent in mammals but is quite distinct in the rat where it takes its origin from the xiphoid process and inserts onto the coracoid process. The sternohumeralis, or sternochondrohumeralis or tensor semivaginae articulationis humeroscapularis, lies in the interval between pectoralis major and pectoralis minor.