240 Region of Shoulder 



lip of the bicipital groove, the clavicular part passing down in front of 

 and below the thoracic part of the muscle. 



Relations. The mamma rests upon its anterior surface ; therefore, 

 in the case of disease of that gland, the arm must be fixed to the side 

 for the sake of perfect rest. Behind it are the ribs and the intercostal 

 muscles ; the subclavius, the costo-coracoid membrane, the pectoralis 

 minor, the axillary vessels, and the brachial plexus. Its outer border lies 

 along the inner edge of the deltoid, an important interval separating 

 them near the clavicle. The cephalic vein is lodged in this inter- 

 muscular groove. 



The pectoralis minor ascends from the third, fourth, and fifth ribs 

 and the intercostal fasciae to its insertion along the thoracic aspect of 

 the coracoid process. It lies beneath the larger muscle, and covers the 

 second part of the axillary vessels, and the brachial plexus. The lowest 

 border of the muscle is subcutaneous, and lies along the fifth rib. 



Suppuration may occur between the two pectoral muscles or 

 beneath them both. In the former case the pus is likely to descend 

 to the lower border of the larger muscle and there to point. In the 

 latter case it may eventually break through the floor of the axilla, or 

 may ascend beneath the costo-coracoid membrane, and along the 

 course of the vessels and nerves, into the neck ; the abscess may 

 possibly find its way through the intercostal spaces unless promptly 

 evacuated. 



Nerves. The two pectoral muscles are supplied by the anterior 

 thoracic branches of the brachial plexus. 



Bursee. There may be a small bursa over the acromion or over 

 the outer end of the clavicle ; a large one between the deltoid and 

 shoulder-joint ; and small ones between the tendons of the infra- 

 spinatus and teres minor and the capsule of the joint, which may com- 

 municate with the interior of the articulation. The bursa sheathing the 

 tendon in the bicipital groove is a continuation of the synovial membrane 

 of the shoulder-joint. A separate bursa intervenes between the tendons 

 of the latissimus dorsi and teres major in the bicipital groove. 



The costo-coracoid membrane is spread between the first rib, 

 clavicle, and coracoid process ; below, it blends with the fascia of the 

 lesser pectoral muscle, and with the sheath which the axillary vessels 

 have brought down from the fascia about the scalene muscles. The 

 membrane and the sheath of the vessels are pierced by the cephalic 

 vein in its course to the axillary vein, and by the acromial thoracic 

 artery. 



The subclavius arises by a tendon from the cartilage of the first 

 rib, and is inserted into the groove on the under surface of the clavicle. 

 It is hidden by the origin of the pectoralis major, the costo-coracoid 

 membrane intervening. Beneath it are the subclavian vessels and 

 the brachial plexus, and when the shoulder is drawn down the muscle 

 closely overhangs the highest part of the axillary vessels. 



