Chap, xi.] THE AXILLA. 183 



towards the skin is arrested by the axillary fascia, its 

 progress backwards by the serratus magnus muscle, 

 which, by its attachment to the scapula, hermetically 

 closes the axillary space behind. In front the 

 advance of the abscess is prevented by the pectoral 

 muscles and clavi-pectoral fascia, while on the inner 

 side is the unyielding thorax, and on the outer side 

 the upper limb. The abscess, therefore, as it fills the 

 axilla pushes forwards the pectoralis major, more or 

 less obliterates the hollow of the armpit, thrusts back 

 the scapula, and widens the angle between the serratus 

 rnagnus and the subscapularis muscles. There is a 

 great tendency, therefore, for unrelieved abscesses to 

 extend upwards into the neck, that being the direction 

 in which the least amount of resistance is encountered. 

 From the neck the purulent collection may extend 

 into the mediastinum. In one case an axillary 

 abscess, set up by shoulder-joint disease, perforated 

 the first intercostal space, and set up fatal pleurisy. 



In opening an axillary abscess, and, indeed, in 

 most incisions into this space, the knife should be 

 entered at the centre of the floor of the axilla, i.e., 

 midway between the anterior and posterior margins, 

 and near to the inner or thoracic side of the space. 

 The vessels most likely to be damaged by an 

 indiscreet incision are the subscapular, running along 

 the lower border of the subscapularis muscle ; the 

 long thoracic, following the lower border of the small 

 pectoral ; and the main vessels lying close to the 

 hnmerus. The knife, if properly entered, should be 

 midway between the two first-named vessels, and 

 quite away from the main trunks. There is an 

 artery (the external mammary) that sometimes comes 

 off as the lowest branch of the axillary trunk, and 

 crosses the middle of the axilla, to be distributed to 

 the thorax below the long thoracic. This vessel would 

 p 'obably be wounded in the incision above named. 



