I028 A MANUAL OF ANATOMY 



of each side unite to form the superior intercostal vein. The right 

 superior intercostal vein, after a downward course, joins the upper 

 part of the right azygos vein. The left superior intercostal vein 

 ascends over the back part of the arch of the aorta, and opens into 

 the left innominate vein. It sometimes receives the left bronchial 

 vein as a tributary. 



Summary of the Intercostal Veins — Right Intercostal Veins. — The first 

 opens into the right innominate vein, or sometimes into the right vertebral 

 vein. The second and third (and, it may be, the fourth also) unite to form 

 the right superior intercostal vein, which opens into the right azygos vein. 

 The lower eight (sometimes the lower seven) are direct tributaries of the 

 right azygos vein. 



Left Intercostal Veins. — The first opens into the left Innominate vein, or 

 sometimes into the left vertebral vein. The second and third (and it may 

 be the fourth also) unite to form the left superior intercostal vein, which 

 opens into the left innominate vein. The fifth, sixth, and seventh (and, it 

 may be, the fourth also) terminate in the upper left azygos vein. The eighth, 

 ninth, tenth, and eleventh are tributaries of the lower left azgyos vein. 



The left superior intercostal vein is developed from two sources. The 

 upper part is formed by the portion of the left primitive jugular vein below, 

 and adjacent to. the commencement of the transverse jugular vein. The 

 lower part is formed by the upper portion of the left cardinal vein. 



Intercostal Glands. — These glands form a chain on either side of the vertebral 

 column, in line with the heads of the ribs. The main glands of each chain lie 

 in the posterior parts of the intercostal spaces, and one or two glands accom- 

 pany each posterior intercostal artery for a very short distance. 



The intercostal glands receive their afferent vessels from (i) the posterior 

 half of the costal pleura, (2) the posterior halves of the external and internal 

 intercostal muscles, (3) the deep muscles of the back, and (4) the spinal canal. 

 Their efferent vessels, on either side, pass to the thoracic duct. 



The efferents of the upper right intercostal glands sometimes open into 

 a right broncho -mediastinal lymphatic trunk, which terminates in the right 

 lymphatic duct. 



The right superior intercostal vein is developed from the anastomotic 

 channels which connect the upper three thoracic segmental veins of the right 

 side. 



Azygos Veins. — ^These are three in number, one right and two 

 left. 



The vena azygos major or right azygos vein commences in the 

 abdomen as the right ascending lumbar vein, and enters the thorax 

 through the aortic opening of the diaphragm, lying on the right 

 side of the aorta, the thoracic duct intervening. It then ascends, 

 under cover of the oesophagus, upon the bodies of the thoracic 

 vertebrae, crossing in its course the right aortic intercostal arteries. 

 Having reached the level of the fifth thoracic vertebra it leaves 

 the vertebral column, and, arching forwards over the right bronchus, 

 it opens into the superior vena cava, just before that vessel pierces 

 the pericardium. In the thorax the right azygos vein continues 

 to lie on the right side of the aorta, the thoracic duct intervening. 



Tributaries. — ^These are as follows : 



1. The right subcostal vein. 



2. The lower seven (sometimes the lower eight) right intercostal 

 veins. 



