THYMIC, TRACHEAL AND CE SOPH AGE AL VEINS 661 



A separate vein frequently passes out from the capsule of the thyreoid gland near the lower 

 part of the lateral lobe, crosses the common carotid, and opens into the main superior thyreoid 

 vein or into the internal jugular vein a little below the cricoid cartilage. In the former case it 

 is regarded as part of the superior thyreoid vein system ; in the latter it is generally known as the 

 middle thyreoid vein. 



The Vertebral Vein 



The vertebral vein [v. vertebralis] does not accompany the vertebral artery in 

 its fourth stage, that is, within the skull, but begins in the posterior' vertebral 

 venous plexus of the suboccipital triangle. It then enters the foramen in the 

 transverse process of the altas, and passes with the vertebral artery through the 

 foramina in the transverse processes of the cervical vertebrae, forming a plexus 

 around the artery. On leaving the transverse process of the sixth cervical verte- 

 bra it crosses in front of the subclavian artery and opens into the innominate vein. 

 It has one or two semilunar valves at its entrance into the innominate vein. In 

 the suboccipital triangle it communicates with the internal vertebral venous 

 plexuses, with the deep cervical, and occipital veins, and is joined by veins from 

 the recti and oblique muscles and the pericranium. 



Tributaries. — As it passes down the neck it receives (1) intervertebral veins, which issue 

 along with the cervical nerves, from the spinal canal; (2) tributaries from the anterior and 

 posterior vertebral venous plexus from the bodies of the cervical vertebrae and their transverse 

 processes; and (3) tributaries from the deep cervical muscles. Just before it terminates in the 

 innominate it is joined by (4) the anterior vertebral vein, a small vein which accompanies the 

 ascending cervical artery, and, sometimes, by the deep cervical vein. 



The Deep Cervical Vein 



The deep cervical vein [v. cervicalis profunda], larger than the vertebral, 

 passes down the neck posterior to the cervical transverse processes. It corre- 

 sponds to the deep cervical artery from which it is separated by the semispinalis 

 cervicis muscle. 



It~begins in the posterior vertebral venous plexus and receives tributaries from the deep 

 muscles of the neck. It communicates with, or entirely drains, the occipital vein by a branch 

 which perforates the trapezius muscle. The deep cervical vein then passes forward beneath 

 the transverse process of the seventh cervical vertebra to open into the innominate vein near 

 the vertebral, or into the latter near its termination. Its orifice is guarded by a pair of valves. 



The Inferior Thyreoid and Thyreoid e a Ima Veins 



The inferior thyreoid veins [vv. thyreoidea inferiores] descend from the lower 

 part of the thyreoid gland obliquely lateralward to the innominate veins. The 

 right vein crosses the innominate 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 termina- 

 tion in the innominate. The left vein passes obliquely over the trachea behind 

 the sterno-thyreoid muscle, and opens into the left innominate vein. It also 

 receives laryngeal and tracheal veins, and sometimes the thyreoidea ima; it is 

 guarded by valves where it opens into the innominate trunk. 



The thyreoidea ima vein [v. thyreoidea ima] is single and placed approximately 

 in the median line. It begins in the thyreoid isthmus from the plexus thjrreoideus 

 impar, runs downward upon the anterior surface of the trachea, and opens into 

 the left innominate vein or into the left inferior thyreoid. 



The Thymic, Tracheal and Esophageal Veins 



These small veins usually open into the left innominate vein. The thymic 

 veins [vv. thymicae], small in the adult, open into the left innominate or into the 

 inferior thyreoid or thyreoidea ima vein. The tracheal veins [vv. tracheales] 

 anastomose with the laryngeal and bronchial veins. The oesophageal veins 

 [w. oesophagese] from the upper part of the oesophagus, anastomose with the 

 lower oesophageal veins and with the pharyngeal plexus. 



