ANTERIOR THORACIC REGION. 



375 



membrane, and internally by the ribs. In this space are seen the axillary 

 vessels and nerves. 



The costo-coracoid membrane should now be removed, when the Subclavius muscle will be 

 seen. 



The Subclavius is a long, thin, spindle-shaped muscle, placed in the interval 

 between the clavicle and the first rib. It arises by a short, thick tendon from 

 the cartilage of the first rib, in front of the rhomboid ligament; the fleshy 

 fibres proceed obliquely outwards, to be inserted into a deep groove on the 

 under surface of the middle third of the clavicle. 



Fir. 237. Muscles of the Chest and Front of the Arm, with the Boundaries of the Axilla. 



Relations. By its upper surface, with the clavicle. By its under surface, it is 

 separated from the first rib by the axillary vessels and nerves. Its anterior 

 surface is separated from the Pectoralis Major by a strong aponeurosis, which, 

 with the clavicle, forms an osteo-fibrous sheath in which the muscle is inclosed. 



[f the costal attachment of the Pectoralis Minor is divided across, and the muscle reflected 

 outwards, the axillary vessels and nerves are brought fully into view, and should be examined. 



Nerves. The Pectoral muscles are supplied by the anterior thoracic nerves; 

 the Subclavius, by a filament from the cord formed by the union of the fifth 

 and sixth cervical nerves. 



Actions. ^ If the arm has been raised by the Deltoid, the Pectoralis Major 

 will, conjointly with the Latissimus Dorsi and Teres Major, depress it to the 

 side of the chest; and, if acting singly, it will draw the arm across the front 

 of the chest. The Pectoralis Minor depresses the point of the shoulder, draw- 



