THE THORACIC WALL. 95 



third; (2) from the long thoracic branch of the axillary artery; (3) from the perforating branches 

 of the upper intercostal arteries. The deep veins accompany the arteries; the subcutaneous 

 veins form a large-meshed network and, in the female, may frequently be seen through the skin. 

 They form the plexus venosus mammilla (circulus venosus Halleri) about the nipple and empty 

 above into the external jugular vein; they also empty into the long thoracic, thoracico-epigastric, 

 and internal mammary veins. 



The lymphatic vessels of the mamma are very numerous and form superficial and deep 

 networks. The greater portion of the lymph drains into the axillary lymphatic glands.* These 

 glands are involved in affections of the mammary gland of the same side, and they are consequently 

 removed together with the breast. In rarer cases they also become involved in affections of the 

 opposite mammary gland, since the lymphatic vessels of both breasts anastomose in the median 

 line. A portion of the lymph passes internally to the intercostal lymphatic vessels and in this 

 manner reaches the lymphatic glands of the thoracic space. 



The deep nerves of the gland accompany the larger lactiferous ducts and are much less 

 numerous than the cutaneous nerves. The cutaneous nerves are furnished partly by the supra- 

 clavicular branches of the cervical plexus, but chiefly by the anterior and lateral cutaneous 

 branches of the second to the sixth intercostal nerves. The connection between the second and 

 third lateral cutaneous branch (intercosto-humeral nerve) and the lesser internal cutaneous nerve 

 explains the occasional occurrence of pain radiating to the region of the elbow or still lower in 

 diseases of the mammary gland (tumors, neuralgia of the mammary gland). In the extirpation 

 of the mammary gland and the diseased axillary tissues the following structures should be par- 

 ticularly avoided: the axillary artery and vein, the long thoracic artery, the subscapular artery, 

 the long subscapular nerve (division produces paralysis of the latissimus dorsi muscle), and the 

 long thoracic nerve (division is followed by paralysis of the serratus magnus muscle) : 



The arteries of the lateral thoracic wall are external and internal. 



The external surface of the lateral thoracic wall is supplied chiefly by the branches of the 

 axillary artery (Fig. 29). The following vessels should be noted: 



1. The acromiothoracic artery, which lies beneath the infraclavicular fossa, where the vessel, 

 together with its numerous branches, is endangered in the ligation of the first portion of the 

 axillary. The vessel arises at the upper margin of the pectoralis minor and immediately divides 

 into a number of branches. The pectoral branches ramify in the muscles of the chest ; if such 

 a branch arises from the axillary higher up (comparatively rare) it is known as the superior 

 thoracic artery. The acromial branch runs transversely outward, perforates the deltoid muscle, 

 and ends in the anastomosis over the acromion. The descending or humeral branch accom- 

 panies the cephalic vein in the groove between the pectoralis major and deltoid muscles. 



2. The long thoracic artery, which arises from the axillary beneath the pectoralis minor 

 muscle. The artery leaves the outer border of this muscle and runs downward to the fifth or 

 sixth intercostal space, somewhat posterior to the margin of the pectoralis major, upon the ser- 



* The lymphatic gland which is usually first involved in carcinoma is situated beneath the border of the pectoralis 

 major muscle'upon the third serration of the serratus magnus (third rib). The lymphatic glands extend upward 

 the axillary vein and beneath the clavicle, in which position their removal is necessarily difficult. Posteriorly, the glai 

 accompany the subscapular artery and the nerves of the same name. 



