AXILLARY SPACE 33 



leaves the axilla and passes into the arm, where it becomes the 

 brachial artery. For convenience of description it is usually 

 divided into three parts the part above, the part behind, and 

 the part below the pectoralis minor, which are known 

 respectively as the first, second, and third parts. The 

 direction which the art'ery takes varies with the position of 

 the limb. When the arm is at a right angle with the body, 

 the direction is that of a straight line from the centre of the 

 clavicle to the middle of the bend of the elbow. When the 

 arm is by the side, the artery describes a curve with the 

 convexity directed laterally; and if the arm is raised above 

 the head the curve formed by the artery is convex in the 

 reverse direction. 



The first part of the axillary artery lies very deeply. It is 

 covered, anteriorly, by the skin, superficial fascia, deep fascia, 

 the clavicular part of the pectoralis major, the costo-coracoid 

 membrane, and the vessels and nerves superficial to it. Even 

 when those are removed the vessel is not completely exposed, 

 because it is enveloped, along with the axillary vein and great 

 nerves, by a funnel-shaped sheath, which is prolonged upon 

 them from the deep cervical fascia (Fig. 12), and it is 

 crossed by the loop of communication between the two 

 anterior thoracic nerves which lies in front of the sheath. 

 Behind this part of the vessel are the first intercostal space 

 and the first digitation of the serratus anterior muscle; the 

 long thoracic nerve and the medial cord of the brachial 

 plexus also cross behind it. To its medial side, and some- 

 what overlapping it, is the axillary vein, whilst above and to 

 its lateral side are the lateral and posterior cords of the 

 brachial plexus. 



The second part of the axillary artery is placed behind 

 the two pectoral muscles, and has the three cords of the 

 brachial plexus disposed around it. The medial cord lies 

 upon its medial side, the lateral cord upon its lateral side, 

 and the posterior cord behind it. The axillary vein is still 

 upon its medial side, but is separated from the artery by the 

 medial nerve-cord. Strictly speaking, it is not in apposition 

 with any muscle posteriorly, being separated from the sub- 

 scapularis muscle by areolo-fatty tissue. 



The third and longest part of the axillary artery is superficial 

 in its distal half, because the anterior wall of the axilla does 

 not extend so far down as the posterior wall. Therefore, 

 VOL. i 3 



