STJBCLAYIAN YEIX. AZYGOS. 469 



artery, viz., the two circumflex and the subscapular veins from the shoulder, 

 the alar vein from the axilla, and the inferior, superior, and acromial 

 thoracic veins from the side of the chest. 



SUBCLAVIAN VEIN; 



The subclavian vein is the continuation of the axillary, but is not like it 

 constantly provided with valves, although a pair may often be found near 

 its termination (Struthers, loc. cit.). It extends from the outer margin of 

 the first rib to the inner end of the clavicle, behind which it terminates by 

 joining with the internal jugular vein to form the innominate or brachio- 

 cephalic vein. The subclavian vein crosses over the first rib and behind the 

 clavicle, not reaching so high up in the neck as the subclavian artery; it is 

 covered by the clavicle, and by the subclavius and sterno-mastoid muscles, 

 and lies on a plane anterior to the artery, from which, while resting on 

 the rib, it is separated by the scalenus anticus muscle and the phrenic 

 nerve. 



TRIBUTARIES. (a). The external and anterior jugular veins (p. 459) 

 open into the subclavian vein on the outer side of the scalenus anticus 

 muscle. 



(6). The vertebral vein, commencing in branches which proceed from the 

 pericranium and the deep muscles lying behind the foramen magnum of the 

 occipital bone, passes outwards and downwards to reach the intertrans verse 

 foramen of the atlas. Through this foramen, and through the canal formed 

 by the corresponding foramina of the other cervical vertebrae, the vein 

 descends with the vertebral artery. Emerging at the foramen in the sixth 

 vertebra, it runs forwards and downwards to join the subclavian vein close 

 to the termination : a small branch sometimes descends through the foramen 

 in the seventh vertebra, and opens separately into the subclavian. The 

 vertebral vein is joined in its course by several branches from the neigh- 

 bouring muscles ; also, immediately before its termination, by a branch 

 corresponding with the deep cervical artery; and in the same situation by 

 another branch of considerable size, which descends in front of the bodies 

 and transverse processes of the vertebrae of the neck, and may be termed 

 the external vertebral vein. It communicates frequently with the spinal 

 veins in the neck, both those on the outer side, and those in the interior of 

 the spinal canal. 



AZYGOS VEINS. 



The azygos veins are longitudinal vessels formed by the union of the 

 veins corresponding to the arteries of the intercostal spaces, and are placed 

 on the sides of the spine. In the lower part of the thorax the two veins of 

 opposite sides are disposed symmetrically, but higher up the blood gathered 

 from some of the veins of the left side is poured into the trunk on the 

 right, which becomes enlarged and unsymmetrical, and has on that account 

 received the name of azygos, while the united lower veins from the corre- 

 sponding parts on the left side constitute the small or left azygos. 



The azygos, or right azygos vein (vena sine pari), commences sometimes 

 by a small branch derived from the inferior cava, where that vessel turns 

 forwards to reach its opening in the diaphragm ; but much more frequently 

 it begins below from the lumbar veins (ascending lumbar) of the right side, 

 and sometimes from the renal vein. Passing from the abdomen into the 

 thorax through the aortic opening in the diaphragm, or to the outer side of 



