AXILLARY SPACE 23 



on the medial wall of the axilla, crosses the interval between 

 the medial and posterior walls, and then runs along the 

 lateral wall to the lower border of the teres major, where 

 it leaves the axilla, and, passing into the arm, 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 of the course of the artery 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 by the skin, superficial fascia, deep fascia, clavicular 

 part of the pectoralis major, the costo-coracoid membrane, and 

 the vessels and nerves superficial to it. But, even when these 

 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, and by the loop of communication 

 between the two anterior thoracic nerves which lies in front of 

 the sheath. Posteriorly, this part of the vessel is supported by 

 the first intercostal space and the first digitation of the serratus 

 anterior muscle, and the long thoracic nerve and the medial 

 cord of the brachial plexus cross behind it. To its medial 

 side, and somewhat overlapping it, is the axillary vein, whilst 

 above and to its lateral side are the lateral and posterior 

 brachial nerve-trunks. 



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. Thus 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 



