THE BREAST AND AXILLA 



29 



To expose the fascia completely, the skin above the incision 

 is dissected upwards and medially until the clavicle and the 

 opposite margin of the sternum are visible ; the skin below the 

 incision is undercut backwards until the level of the posterior 

 wall of the axilla is reached, and downwards until the sheath 

 of the rectus abdominis and the upper digitations of the external 

 oblique are well exposed. 



The Pectoralis Major arises by a Clavicular Head from the 

 front of the medial third or more of the clavicle and by a Costo- 

 sternal Head from the front of the sternum, from the aponeurosis 

 of the external oblique, and from the upper five or six costal 

 cartilages. These two heads of origin remain quite distinct 

 from one another almost to the insertion into the lateral lip of 

 the inter-tubercular sulcus (bicipital groove). The pectoralis 

 major is a powerful adductor, and it helps in flexion and medial 

 rotation of the humerus. It is supplied by the lateral and 

 medial anterior thoracic nerves (C. 5, 6, and 7, C. 8 and T. i). 



If the clavicular head is preserved in the operation of complete 

 excision of the breast, no movements are lost, although the 

 arm is weakened by the removal of the costo-sternal portion. 



The deep stratum of the anterior wall of the axilla is formed 

 by the clavi-pectoral fascia, the pectoralis minor, and the 

 subclavius. 



The Pectoralis Minor arises from the bony sternal extremities 

 of the third, fourth, and fifth ribs, under cover of the pectoralis 

 major, and runs upwards and laterally to be inserted into the 

 medial border of the coracoid process. It is supplied by the 

 medial anterior thoracic nerve (C. 8 and T. i), from the medial 

 cord of the brachial plexus. The nerve pierces the muscle 

 about i inches from its insertion and enters the pectoralis 

 major. The pectoralis minor helps in forward and downward 

 movements of the shoulder girdle ; and, when the scapula is 

 fixed, it acts as an elevator of the ribs. 



The Subclavius, which lies between the clavicle and the 

 first rib, is supplied by a small nerve which is formed by twigs 

 from C. 5 and C. 6. It helps to steady the clavicle in movements 

 of the shoulder, by pulling it medially towards the sternum. 



The Clavi-Pectoral Fascia extends from the clavicle above 

 to the axillary fascia below. It forms the fascial sheath of the 

 subclavius, and is attached to the edges of the groove for that 

 muscle on the clavicle. The layers enclosing the subclavius 

 fuse at its lower border to form the costo-coracoid membrane, 



