CHAPTER IV. 

 AXILLA, 



ANATOMY. STRUCTURES. 



ACTION OF MUSCLES. LANDMARKS. 

 AXILLARY FASCIAE. OPERATIONS. 



Anatomy. The axilla is a space, irregularly pyra- 

 midal in form, and serves for the passage of delicate struc- 

 tures to and from the trunk. It has a base, an apex, and 

 four unequal sides. The base is directed downwards and 

 is protected by the integument and superficial fascia and 

 by a strong layer of fascia, "axillary fascia proper ," passing 

 from the lower border of the pectoralis major backwards 

 to the lower border of the latiss. dorsi. The base is wide 

 internally, but narrow externally on account of the con- 

 vergence of these muscles towards their insertion into the 

 humerus. The apex> directed upwards, corresponds to 

 the triangular interval between the first rib internally, the 

 clavicle anteriorly and the upper border of the scapula 

 posteriorly. 



Through it the axillary artery, the brachial plexus of 

 nerves, and the external respirator} 7 of Bell enter, while 

 the axillary vein and the lymphatics leave the axilla. 



Boundaries. In front the axilla is bounded by the 

 integument, fasciae, the pectoralis major, pectoralis 

 minor, clavipectoral fascia and the subclavius muscle; 

 internally, by the four or five upper ribs with the inter- 

 costal muscles between, and by the corresponding serra- 

 tions of the serratus magnus. Postero-externally the 

 structures are the subscapularis, the teres major and the 

 latiss. dorsi, while externally are the humerus, thecoraco- 

 brachialis and the biceps muscle. 



Muscles. The pectoralis major is worthy of more 

 than a passing notice because of the peculiar manner of 



