PRACTICAL CONSIDERATIONS: AXILLA AND SHOULDER. 5S1 



muscle (which it invests), forms the floor of the so-called superficial infraclavicular 

 triangle, the roof of which is made by the clavicular fibres of the great pectoral, the 

 base by the anterior fibres of the deltoid, the upper side by the sternal half of the 

 clavicle, and the lower side by a line parallel to the uppermost sternal fibres of the 

 great pectoral. Its apex is at the sterno-clavicular angle of junction. The floor of 

 this space is pierced by the external anterior thoracic nerve, the acromio-thoracic 

 vessels, and the cephalic vein (Fig. 556). Fat containing a few lymphatic glands, 

 often involved in carcinoma of the breast, is found there. It is closed in above by 

 the clavicle, but is continuous below with the space between the two pectoral muscles 

 down to the level where the superficial layer of the deep fascia and the clavi-pectoral 

 fascia (which has invested the pectoralis minor and continued downward as a single 

 layer again) unite at the lower border of the pectoralis major to form the axillary 

 fascia. Effusions of blood or collections of pus occupying this space between the two 

 muscles are therefore prevented from passing upward by the clavicle, forward by the 

 pectoralis major, and backward by the clavi-pectoral fascia and pectoralis minor. 



Fig. 564. 



Humeral branch of acromio-thoracic artery 



Pectoralis minor \ „ , 



Deltoid ^.-^'"'^ ^>!^. \ 



Pectoralis major, 

 distal stump 



\ 



lalic vein 



Cut edge of-^ 

 superficial pec- 

 toral fascia 



Axillary artery 

 and vein 



Cut edge of superficial layer o 

 clavi-pectoral fascia 



Teres major covered by axillary fascia 



Pectoralis major, 

 clavicular origin 



Costo-coracoid 



membrane 



Deep layer of 



clavi-pectoral 

 fascia 



Thoracic branch 



of acromio- 

 thoracic artery 



Pectoralis minor, 

 cut edge 



Dissection of thoracic wall; pectoralis minor has been partly removed, exposing deep layer of clavi-pectoral 



fascia. 



Consequently they are apt to approach the surface near the anterior axillary margin 

 or in the groove between the great pectoral and deltoid, — i.e., at either the lower 

 border of the sternal portion of that muscle or the upper border of its clavicular fibres. 

 Beneath the costo-coracoid membrane is a region described as the deep infra- 

 clavicular triangle. Although continuous with the axilla, this space is conveniently 

 studied as a separate region on account of the important structures which it contains 

 and the frequency with which it is invaded by disease. Its floor is formed by the 

 first and second ribs and the intercostal, serratus magnus, and subscapularis muscles. 

 Its apex is at the angle made by the line of the upper border of the small pectoral 

 and that of the clavicle at the coracoid process, those two lines constituting its sides. 

 The base is towards the sternum at the line where the costo-coracoid membrane is 

 fused with the deep fascia over the upper intercostal spaces. Through this triangle 

 pass the axillary, superior thoracic, and acromio-thoracic vessels, the cephalic vein, 

 the external and internal anterior thoracic and long thoracic nerves, and the brachial 

 plexus. It contains fat, with numerous lymphatic glands and vessels. It is obvious 



