628 THE VEINS 



near the lower part of the lateral lol)e of that body, crosses the common carotid 

 ohliquelv downwards and outwards, and opens into the internal jugular vein a 

 little below the cricoid cartilagi\ 



The Inferior Thyroid Veins 



The inferior thyroid veins descend from the lower part of the thyroid body 

 obliquely outwards to the innominate veins. The right vein crosses the innom- 

 inate artery just before its bifurcation, and ends in the right innominate vein 

 a little above the superior vena cava. It receives inferior laryngeal veins and 

 veins from the trachea, and has valves at its termination in the innominate. 

 The left vein passes obliquely over the trachea behind the sterno-thyroid muscle, 

 and opens into the left innominate vein. It also receives laryngeal and tracheal 

 veins, and is guarded l:)y valves where it opens into the innominate trunk. 

 The inferior thyroid veins communicate across the trachea by transverse branches. 

 Not unfrequently the inferior thyroid veins (right and left) unite to form a single 

 trunk which joins the left innominate vein. 



The Vertebral Veins 



The vertebral vein (fig. 342) does not accompany the vertebral artery in its 

 fourth stage, that is, within the skull, but begins as a plexus of small veins in the 

 suboccipital triangle. It then enters the foramen in the transverse process of the 

 atlas, and passes with the vertel^ral artery through the foramina in the transverse 

 processes of the cervical vertebrEe, forming a plexus around the artery. On leav- 

 ing the transverse process of the sixth cervical vertebra it crosses in front of the 

 subclavian artery and opens into the innominate vein. It has one or two semi- 

 lunar valves at its entrance into the innominate vein. In the suboccipital triangle 

 it communicates with the intraspinal, deep cervical, and occipital veins, and is 

 joined by veins from the recti and oljlique muscles and the pericranium. Tribu- 

 taries. — As it passes down the neck it receives (1) lateral spinal veins, which 

 issue along with the cervical nerves and lateral spinal arteries from the spinal 

 canal; (2) branches from the venous plexus about the bodies of the cervical verte- 

 brae and their transverse processes; (3) branches from the deep cervical muscles: 

 and (4) branches from the cervical dorsal spinal veins. Just before it terminates 

 in the innominate it is joined by (5) the deep cervical vein (sometimes); (6) the 

 anterior vertebral vein; and (7) the upper superior intercostal vein (sometimes). 



The anterior vertebral vein begins in a plexus in front of the bodies of the 

 cervical vertebri:e, and, running downwards with the ascending cervical artery 

 between the scalenus anticus and longus colli muscles, opens into the vertebral vein 

 just before the latter ends in the innominate. It receives tributaries from the 

 scaleni, longus colli, and rectus capitis anticus muscles. 



The deep cervical vein, which is really a part of the posterior superficial vein 

 of the scalp, is described with that vein (page 614). 



3. THE SPINAL VEINS 



The spinal veins, which form plexuses around and within the spinal canal from 

 the cranium to the sacrum, may be divided into the extra- and intraspinal veins. 

 The extraspinal form a plexus both in front of the bodies of the vertebrae (the 

 anterior spinal plexus), and in tlie sidnal groove between the transverse and 

 s]»inous ))rocesscs — the dorsal plexus, or dorsal spinal plexus as it is often 

 called. The intraspinal veins, or those within the spinal canal, may be divided 



4 



