THE VEETEBEAL VEINS. 963 



they fuse into a single vessel which enters the superior mediastinum and ends in the 

 innominate vein of the s,ame side. 



The tributaries of the internal mammary veins are (a) The venae 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, (b) Six anterior 

 perforating veins which accompany the corresponding arteries, one lying in each of the 

 upper six intercostal spaces, (c) 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. 



Venae Epigastricae Superiores The Superior Epigastric Veins. The venae 

 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, between the sternal and costal origins of the diaphragm, and 

 terminate in the internal mammary veins. 



Musculo-phrenic Veins. The venae comites of the musculo-phrenic artery com- 

 mence in the abdomen, pass through the diaphragm with the musculo-phrenic artery, 

 and terminate in the internal mammary veins. They receive as tributaries the anterior 

 intercostal veins of the seventh, eighth, and ninth intercostal spaces, and small venules 

 from the substance of the diaphragm and walls of the abdomen. 



Venae Vertebrales The Vertebral Veins correspond only to the extra-cranial 

 parts of the vertebral arteries. Each commences by the union of offsets from 

 the intraspinal venous plexuses, and, issuing from the vertebral canal, passes 

 across the posterior arch of the atlas, with the vertebral artery, to the foramen in 

 the transverse process of the atlas. In the foramina in the cervical transverse 

 processes, a plexus of venous channels surrounds the artery. At the lower part 

 of the neck efferents from the plexus unite to form a single trunk which issues 

 from the foramen in the transverse process of the sixth cervical vertebra, and 

 descends, in the interval between the longus colli and scalenus anterior muscles, 

 to terminate in the upper and posterior part of the innominate vein; at its 

 termination there is a uni- or bi-cuspidate valve. 



Relations. In the first part of its course the vein lies in the sub-occipital triangle. 

 The second, plexiform portion, is in the canal formed by the foramina in the transverse 

 processes of the cervical vertebrae, and, with the artery, which it surrounds, lies anterior 

 to the trunks of the cervical spinal nerves. The third part, in the root of the neck, is 

 between the longus colli and scalenus anterior muscles, in front of the first part of the 

 vertebral artery, and behind the internal jugular vein. 



Tributaries. In addition to the offsets from the intraspinal venous plexuses by the 

 union of which it is formed, each vertebral vein receives the following tributaries : (a) 

 Small vessels which issue from the muscles, ligaments, and bones of the deeper parts of the 

 neck, and the lower and posterior part of the head, (b) Offsets from the intraspinal venous 

 plexuses which pass out of the vertebral canal by the intervertebral foramina. (c) The 

 ascending cervical vein, a vessel which is formed by the union of tributaries which issue 

 from a venous plexus on the anterior aspects of the bodies and roots of the transverse 

 processes of the cervical vertebrae. This vessel accompanies the ascending cervical artery, 

 and terminates in the lower part of the vertebral vein, immediately after the latter has 

 issued from the foramen in the sixth cervical transverse process, (d) The deep cervical 

 vein ; this commences in the sub-occipital triangle from a venous plexus with which 

 the vertebral and occipital veins communicate. It descends, posterior to the transverse 

 processes of the cervical vertebrae, in company with the profunda cervicis artery, turns 

 forwards at the root of the neck, between the transverse processes of the sixth and 

 seventh cervical vertebrae or between the latter and the neck of the first rib, and opens 

 into the vertebral vein. It receives blood from the muscles, ligaments, and bones of the 

 back of the neck, (e) The posterior intercostal vein from the first intercostal space some- 

 times opens into the vertebral vein. 



Occasionally the venous plexus around the vertebral artery ends below in two terminal 

 trunks, anterior and posterior, instead of one. In those cases the second terminal vessel 

 lies behind the lower part of the vertebral artery, passes through the foramen in the 

 transverse process of the seventh cervical vertebra, and turns forwards on the lateral side 



62 a 



