40 Anatomy Applied to Medicine and Surgery. 



three parts by the pectoralis minor, viz., the first part 

 above, the second beneath, and the third below this 

 muscle. The vein is also divided by the pectoralis minor 

 into three parts, but these are numbered in the inverse 

 order to those of the artery. When the arm hangs by the 

 side the vein lies partly in front but chiefly to the inner 

 side of the artery, but when the limb is at right angles to 

 the body it overlaps the artery, i.e. y lies principally in 

 front of it. Both artery and vein are enclosed in the 

 axillary sheath, a prolongation downwards of the cervical 

 fascia. The vein is adherent to this sheath and the 

 sheath to the costo-coracoid membrane which lies in front 

 of it. The artery supplies the muscles and adipose tissue 

 of the axilla by means of the superior thoracic and acro- 

 mio-thoracic branches from the first part ; the alar and 

 long thoracic from the second part ; the subscapular and 

 the anterior and posterior circumflex from the third part, 

 while an occasional branch is given off to supply the 

 superficial structures of the lower part of the thorax, viz., 

 superficial external mammary artery. 



The adipose tissue of the axilla is of a pinkish hue and 

 is more granular here than elsewhere. It is of special 

 support to the axillary vein, since oedema of the limb has 

 occurred from phlebitis developing as the result of the re- 

 moval of this tissue in the complete operation for the re- 

 lief of mammary cancer. 



The netves of the axilla are derived from the brachial 

 plexus by branches from the 5th, 6th, yth, 8th cervical 

 and first dorsal nerves. They form a plexiform network 

 in the neck, but the plexus is narrow where it passes 

 under the clavicle, and, about the coracoid, it breaks up 

 into branches for the supply of the limb. The pectoral 

 muscles are supplied by the anterior (internal and exter- 

 nal) thoracics, the subscapularis by the upper and lower 



