828 THE VASCULAR SYSTEM. 
major. It receives the left bronchial veins, some small posterior mediastinal veins also 
open into it, and it communicates with the left superior intercostal vein. 
The vena azygos minor inferior (y. hemi-azygos) commences in the epigastric region. 
At its origin it is connected either with the left ascending lumbar vein or with the left renal 
vein. After piercing the left crus of the diaphragm it ascends on the left sides of the 
bodies of the lower dorsal vertebrze, and opposite the eighth dorsal vertebra it turns to the 
right, crosses the front of the spine behind the aorta, cesoph agus, and thoracic duct, and 
terminates in the vena azygos major. As it ascends in the posterior mediastinum it 
lies internal to the sympathetic cord, behind the roots of the splanchnic nerves, and 
superficial to the lower left intercostal arteries. Through the left ascending lumbar 
vein it receives blood from the upper lumbar veins of the left side; the lower four 
posterior intercostal veins, the left subcostal vein, and small mediastinal tributaries also 
terminate in it. 
Not infrequently the upper and lower minor azygos veins unite, opposite the seventh 
or eighth dorsal vertebra, to form a common trunk which terminates in the azygos major. 
The bronchial veins do not quite correspond to the bronchial arteries, and they are 
not found on the walls of the smallest bronchi. On each side the tributaries run in front 
of and behind the bronchial tubes to the root of the lung, where they unite, as a rule, 
into two small trunks; those of the right side open into the vena ALY SOS major, and those 
of the left into the vena azygos minor superior, or into the left superior intercostal vein. 
On both sides they are joined by tracheal and posterior mediastinal veins. Some few 
small bronchial veins, including most. of those from the smaller tubes, open into the 
pulmonary veins. 
Intercostal Veins.—There are two sets of intercostal veins (vv. intercostales), the 
anterior and the posterior. 
The anterior intercostal veins are tributaries of the internal mammary or of the 
musculo-phrenic veins, and are described with those vessels (p. 829). 
The posterior intercostal veins (Fig. 592) are eleven in number on each side. <A 
single vein runs in each intercostal space ; it is situated in the subcostal groove above the 
corresponding artery. 
On the right side the posterior intercostal vein of the first space accompanies the 
superior intercostal artery across the front of the neck of the first rib, and terminates 
in the vertebral or innominate vein. The second, third, and fourth intercostal veins of 
the right side unite together to form a common trunk, the right superior intercostal vein 
(v. intercostalis suprema dextra), which terminates by joining the vena azygos major. The 
fifth to the eleventh posterior intercostal veins of the right side open ‘separately i in the 
vena azygos major. 
On the left side the first posterior intercostal vein follows a course similar to that 
taken by the corresponding vein on the right side, and terminates in the left vertebral or 
innominate vein. The second, third, and fourth posterior intercostal veins of the left side 
unite to form the left superior intercostal vein (v. intercostalis suprema sinistra), which 
runs from behind forwards along the left and anterior aspect of the aortic arch. It passes 
obliquely between the left vagus and phrenic nerves, crosses the root of the left 
subclavian artery, and ends in the lower part of the lett innominate vein. The fifth, 
sixth, seventh, and eighth posterior intercostal veins of the left side terminate in the 
vena azygos minor superior, and the ninth, tenth, and eleventh in the vena ALY QOS minor 
inferior. 
Each posterior intercostal vein is provided with valves, both at its termination and 
along its course, which prevent the blood flowing towards the anterior aspect of the 
thoracic wall. Its tributaries are derived from the adjacent muscles and bones, and a 
short distance from its termination it receives a dorsal tributary which passes forwards 
to it between the transverse processes of the vertebrae. This dorsal vessel is formed by 
the union of small veins which issue from the muscles of the back, from the anterior and 
posterior spinal plexuses which lie respectively in front of the bodies and behind the 
arches of the vertebrae, and by venous channels which issue through the intervertebral 
foramina ; the latter vessels commence in the spinal canal, where they are connected with 
the anterior and posterior spinal veins. 
THE INNOMINATE VEINS 
The innominate or brachio-cephalic veins (vv. anonyme dextra et sinistra, 
Figs. 551 and 552), two in number, right and left, return blood from the head and 
neck, the upper extremities, the upper part of the posterior wall of the thorax, the 
