THE INNOMINATE VEINS. 



511 



sternum. The right vein is about an inch in length, and descends nearly vertically 

 by the side of the commencement of the subclavian and the upper end of the 

 innominate artery ; externally it is covered by the right pleura and lung, the 



Fig. 400. SKETCH OP THE PRINCIPAL VENOUS TRUNKS, 



TOGETHER WITH THE THORACIC DUCT. (Allen Thomson.) 



a, basilar process of occipital bone, through which and the 

 temporal bones a transverse section has been made so as to lay 

 open the jugular foramen on both sides ; 6, fifth cervical ver- 

 tebra ; c, first rib ; d, the sixth ; e, the twelfth ; /, fifth lumbar 

 vertebra; 1, superior vena cava divided at the place of its 

 entrance into the right auricle ; 2, right, 2', left subclavian 

 vein ; 3, right internal jugular vein ; 3', 3', lower parts of the 

 lateral sinuses of the dura mater ; that of the right side shows 

 at its junction with the jugular vein the bulb which lies in the 

 jugular fossa of the temporal bone ; 4, right, and 4', left external 

 jugular vein ; 5, right, and 5', left vertebral vein, being joined 

 by 5", the anterior vertebral vein, before entering (in this case) 

 the subclavian vein ; 6, placed on the left subclavian vein 

 below the opening of the last, and of the thoracic duct ; below 

 b, the inferior thyroid veins ; 7, 7', internal mammary veins ; 

 8, the left superior intercostal vein, joining the left innominate, 

 and anastomosing below with the left upper azygos vein ; the 

 right superior intercostal vein is seen joining the large azygos 

 vein ; 9, 9, 9, large azygos vein ; 9', left lower azygos vein ; 

 10, thoracic duct ; 11, inferior vena cava, at the place of junc- 

 tion of the renal veins ; 12, communication of the left lower 

 azygos vein with the left renal vein ; 13, 13', right and left 

 ascending lumbar veins, continued upwards into the corre- 

 sponding azygos veins ; 14, 14', external iliac veins, which are 

 joined higher up by the internal iliacs, to form the common 

 iliac veins ; 15, placed on the promontory of the sacrum, points 

 on either side to the prolongation of the lower branches of 

 the lumbar veins into the pelvis, and their union with sacral 

 and other branches of the internal iliac veins. 



phrenic nerve being interposed. The vein of the 

 left side, nearly three times as long as the right, 

 takes a course from left to right, at the same time 

 inclining somewhat downwards : it crosses behind 

 the upper part of the manubrium, being separated 

 from the bone by the lower ends of the sterno- 

 hyoid and sterno- thyroid muscles, and by the 

 thyinus gland or its remains ; below it is the arch 

 of the aorta, and behind it are the three large 

 branches of the arch, as well as the left phrenic 

 and pneumo-gastric nerves. The innominate veins 

 have no valves. 



LATERAL TRIBUTARIES. Both innominate 

 veins are joined by the vertebral, inferior thyroid 

 and internal mammary veins ; that of the left 

 side also by the superior intercostal, and some 

 small thymic, mediastinal and pericardial veins. 

 There is also, opening into the angle of union 

 of the internal jugular and subclavian veins, 

 on the left side the thoracic duct, on the right side the right lymphatic duct. 



The vertebral vein results from the union of a considerable offset from the 

 intraspinal venous plexus, issuing above the neural arch of the atlas, with branches 

 which proceed from the pericranium and the deep muscles lying behind the 

 foramen magnum of the occipital bone, and which anastomose with the occipital, 



