262 THE VASCULAR SYSTEMS 



artery; a branch supplies the shoulder-joint, and another the 

 subscapular fossa. 



3. The transverse cervical divides at the anterior border of the 

 trapezius into a superficial cervical branch, ascending beneath 

 and supplying that muscle, and a posterior scapular running 

 along the posterior border of the scapula to join the subscapular 

 artery at its inferior angle. 



III. The internal mammary descends from the under surface 

 of the subclavian opposite the thyroid axis along the hinder 

 surface of the costal cartilages, ^ inch from the sternum, as far 

 as the sixth interspace, and divides into the musculophrenic and 

 superior epigastric. At first, behind the subclavian vein and the 

 phrenic nerve, it lies against the pleura, but separated from it 

 below by the triangularis sterni. 



Branches. (a) Comes nervi phrenici, to the diaphragm along 

 with the nerve, joins the phrenic arteries; (b) mediastinal; (c) 

 pericardiac; (d) sternal; (e) anterior intercostal; (/) anterior or 

 perforating; (g) musculophrenic; (h) superior digastric. 



IV. The superior intercostal crosses in front of the neck of the 

 first rib, and supplies the first and part of the second interspace. 



Its profunda cervicis branch passes backward between the 

 seventh cervical vertebra and the first rib, ascends under the 

 complexus to the axis, and joins the princeps cervicis and ver- 

 tebral arteries. 



THE ARTERIES OF THE UPPER EXTREMITY 



The Axilla 



The axilla is a four-sided pyramidal space, of which the sides 

 are unequal, situated between the upper lateral aspect of the 

 chest and the arm. Its apex is between the first rib, the clavicle, 

 and the upper margin of the scapula. The base is directed down- 

 ward and outward, and is formed by the skin and fascia stretch- 

 ing across between the pectoralis major and the latissimus dorsi. 

 The anterior wall is formed by the pectoral muscles, the costo- 

 coracoid membrane, the clavicle, and the subclavius muscle. 

 The posterior wall extends lower than the anterior, and is formed 

 by the subscapularis above, the teres major and latissimus below. 

 The inner wall is convex. It is formed by parts of the first four 



