THE INNOMINATE VEINS. 829 
anterior wall of the thorax, and the upper part of the anterior wall of the abdomen. 
Each innominate vein commences behind the sternal end of the clavicle of the 
corresponding side, and is formed by the union of the internal jugular and sub- 
clavian veins; the two innominate veins terminate by uniting together, behind the 
lower border of the cartilage of the first rib on the right side, to form the superior 
vena cava. ‘To reach this point the left vein has to pass from left to right behind 
the manubrium sterni, and it is therefore about three times as long as the right 
vein. The innominate veins do not possess valves. 
The right innominate vein is a little more than one inch (3 cm.) in length. 
It descends almost vertically to the lower border of the first costal cartilage, and 
terminates in the superior vena cava. 
Relations.—It is overlapped in front by the right lung and pleural sac, and is in 
relation with the sternal end. of the clavicle and the sterno-hyoid and sterno-thyroid 
muscles. It partly overlaps the innominate artery, which lies to its left side, and it is in 
front of the right vagus nerve and the posterior part of the upper end of the right pleural 
sac. The phrenic nerve and the accompanying vessels run along its right side, and inter- 
vene between it and the right pleural sac. 
Tributaries.—In addition to the veins by the union of which it is formed, the right 
innominate vein receives the right vertebral and internal mammar y veins, and sometimes 
the right inferior thyroid vein ‘and the first right posterior intercostal vein. The right 
lymphatic duct also opens into it. 
The left innominate vein passes from left to right, with a shght obliquity 
downwards, behind the upper part of the manubrium sterni, to the lower border 
of the first right costal cartilage, where it terminates in the superior vena cava 
It is a little less than three inches long (6 to 7:5 em.). 
Relations.—It is covered in front, in the greater part of its extent, by the left pleura, 
but at its right extremity it is slig tly OV erlapped by the right pleura, and in the middle 
line the remains of the thymus oli und intervene between it and the posterior surface of the 
sternum. It rests poster iorly upon the left subclavian artery, the left phrenic, and the left 
vagus nerves, the left superior cardiac branch of the sympathetic, the inferior cervical 
branch of the left vagus, the left common carotid artery, the trachea, and the innominate 
artery. 
Its lower border is in relation with the arch of the aorta, and on its upper border it 
receives the inferior thyroid vein of one or both sides. 
Tributaries.— It receives the vertebral, internal mammary, inferior thyroid, and 
superior intercostal veins of its own side, the first left posterior intercostal vein, and 
some pericardial, thymic, anterior bronchial, and anterior mediastinal veins. Sometimes 
the right inferior thyroid vein joins it, but usually this vessel terminates in the right 
innominate vein or in the commencement of the superior vena cava. 
The thoracic duct opens into it just at the angle of junction of the internal jugular 
and subclavian veins. 
Internal mammary veins (vv. mammariz interne).—Each internal mammary 
artery is accompanied by venze comites; they commence by the union of the vene 
comites of the superior epigastric and musculo-phrenic arteries, between the sixth costal 
cartilage and the triangularis sterni, and at the upper part of the thorax they fuse into a 
single vessel which enters the superior mediastinum and ends in the innominate vein of the 
same side. 
The tributaries of the internal mammary veins are—(a) The vene comites of the 
superior epigastric and musculo-phrenic arteries, which in their turn receive tributaries 
which correspond with the branches of the arteries they accompany. (4) Six anterior 
perforating veins which accompany the corresponding arteries, one lying in each of the 
upper six intercostal spaces. (¢) Twelve anterior intercostal veins from the upper six 
intercostal spaces, two veins lying in each space with the corresponding branches of the 
internal mammary artery. (d) Small and irregular pleural, muscular, mediastinal, and 
sternal veins. 
The internal mammary veins are provided with numerous valves which prevent the 
blood from flowing downwards. 
Superior epigastric veins (vv. epigastricze superiores).—The venz comites of the 
superior epigastric artery receive tributaries from the substance of the rectus abdominis, 
the sheath of the muscle, and the superjacent skin and fascia; they pass with the artery, 
