THE VERTEBRAL VEINS. 315 



tensive. It commonly originates from the posterior and infe- 

 rior part of the subclavian opposite to the origin of the verte- 

 bral, and is generally distributed to the first and second inter- 

 costal spaces, but rarely to the third. 



The Left Intercostal frequently originates near the left 

 internal mammary, and sometimes in common with it. It 

 descends behind the aorta on the left of the spine, and com- 

 monly sends off the six upper intercostal veins, of which the 

 two or three superior pass upwards from a part of the vein 

 which is opposite to the third dorsal vertebra. Its extent is 

 very difierent in different subjects. In some instances it passes 

 so low as to supply the seventh or eighth intercostal space. 

 This vein also gives off the Left Bronchial Vein, which sends 

 branches to the oesophagus and bronchial glands. 



The Vertebral Veins 



Arise from the subclavians, but sometimes they proceed 

 differently in different subjects : the right passing behind, and 

 the left before the subclavian artery of its respective side. 

 Each of them, however, becomes contiguous to its correspond- 

 ing artery. When it has arrived at the place in the transverse 

 processes, where the artery enters the vertebral canal, it sends 

 off an external branch, which passes up before, and nearly in 

 contact with those processes, and gives ramifications to the 

 contiguous muscles, and also to the cavity of the spine. These 

 last mentioned ramifications enter by the lateral apertures 

 between the transverse processes, and anastomose with the 

 veins and sinuses of the cavity. The branch often finally ter- 

 minates in the lateral sinus of the dura mater, by passing 

 through the foramen near the mastoid process of the temporal 

 bone. The Main TrunJc of the vertebral vein generally sends 

 off another external branch to the muscles near the basis of 

 the neck, and afterwards enters the canal with the vertebral 

 artery. While in this canal, it generally sends off two branches 

 through each of the lateral apertures between the vertebrae. 

 One of these branches passes backwards to the muscles of the 

 neck, and the other proceeds into the great spinal cavity, and 

 communicates with the venous sinuses. 



