668 



THE VEINS. 



and join to form a trunk which ends in the right azygos vein or in the left lower 

 azygos. It sometimes receives the left bronchial vein. When this vein is small 

 or altogether wanting, the left superior intercostal vein will extend as low as the 

 fifth or sixth intercostal space. 1 



Surgical Anatomy. In obstruction of the superior vena cava the azygos veins are one of 

 the principal means by which the venous circulation is carried on, connecting as they do the superior 

 and inferior venae cavae. and communicating with the common iliac veins by the ascending lumbar 

 veins, and with many of the tributaries of the inferior vena cava. 



The bronchial veins return the blood from the substance of the lungs ; that of 

 the right side opens into the vena azygos major near its termination ; that of the 

 left side, into the left superior intercostal vein or left upper azygos vein. 



THE SPINAL VEINS. 



The numerous venous plexuses placed upon and within the spine may be 

 arranged into four sets : 



1. Those placed on the exterior of the spinal column (the dorsi-spinal veins). 



2. Those situated in the interior of the spinal canal, between the vertebrae and 

 the theca vertebralis (meningo-rachidian veins). 



3. The veins of the bodies of the vertebrae (venae basis vertebraruni). 



4. The veins of the spinal cord (medulli-spinat). 



1. The Dorsi-spinal Veins commence by small branches which receive their 



The dor si- spinal veins. 



FIG. 389. Transverse section of a dorsal vertebra, showing the spinal veins. 



blood from the integument of the back of the spine and from the muscles in the 

 vertebral grooves. They form a complicated network, which surrounds the spinous 

 processes, the laminae, and the transverse and articular processes of all the ver- 

 tebrae. At the bases of the transverse processes they communicate, by means of 

 ascending and descending branches, with the veins surrounding the contiguous 

 vertebrae, and they join with the veins in the spinal canal by branches which 

 perforate the ligamenta subflava. Other branches pass obliquely forward, 

 between the transverse processes, and communicate with the intraspinal veins 

 through the intervertebral foramina. They terminate by joining the vertebral 



1 For an account of the arrangement of the azygos and superior intercostal veins in a number of 

 consecutive cases from the same dissecting-room, see a paper by Mr. B. G. Morison (Jom~nal of Anat- 

 <)my and Physiology, vol. xiii. p. 346). The most important difference between his description and that 

 in the text is, that he always found two superior intercostal veins on both sides, the vein from the first 

 space being separate, and joining the corresponding innominate vein. The lower (and larger) supe- 

 rior intercostal vein he describes as opening into the azygos on the right and innominate on the left 

 side. 



