14 



THE UPPER EXTREMITY 



the anterior wall. It is formed, from above downwards, by 

 the subscapularis muscle, the tendon of the latissimus dorsi, 

 and the teres major muscle. The subscapularis, covering the 

 costal surface of the scapula, takes by far the largest share 

 in the formation of this wall. The narrow tendon of the 

 latissimus dorsi conceals the front of the teres major and 

 only the lower border of the latter muscle is seen below it. 

 The posterior fold of the axilla is formed by the lower border 

 of this wall. 



The medial wall is constituted by the upper four or five 

 ribs with the intervening intercostal muscles ; it is clothed by 

 the corresponding digitations of the serratus anterior muscle. 



The lateral wall is formed by the humerus and the conjoined 



9 10 J38 4 



1. Upper end of humerus. 



2. Scapula. 

 3- Rib. 



4. Pectoralis major. 



5. Serratus anterior. 



6. Subscapularis. 



7. Axillary vein. 



8. Axillary artery. 



9. Long head of biceps. 



10. Conjoined origin of 



short head of biceps 

 and coraco-brachi- 

 alis. 



11, 12, 13. Brachial nerves. 



FIG. 6. Diagram of section through the Axilla of the Left Side. 



proximal parts of the coraco-brachialis and short head of the 

 biceps brachii. 



The apex of the space corresponds with the narrow com- 

 munication between the axilla and the root of the neck. It 

 is a triangular interval (which can readily be investigated by 

 the finger when the space is dissected) bounded by the 

 clavicle, first rib, and upper margin of the scapula, and 

 through it pass the great axillary vessels and brachial nerves 

 on their way from the neck to the arm. The wide base of 

 the axilla is closed by the vaulted axillary fascia. 



Contents of the Axilla. The axillary artery and vein, 

 with the great brachial nerves and the axillary lymph vessels 

 and lymph glands, constitute the most important contents 

 of the axilla. Except at the summit of the space, they lie 

 close to the lateral wall, and follow it in all the movements 

 of the arm. 



Dissection. Cut through the clavicular fibres of the pectoralis major, 



