Inferior thyroid veins
The inferior thyroid veins two, frequently three or four, in number, arise in the venous plexus
Venous plexus
A venous plexus is a congregation of multiple veins.Examples of venous plexuses are:* Vesical venous plexus* Vaginal venous plexus* Uterine venous plexus*Pterygoid plexus...

 on the thyroid gland, communicating with the middle
Middle thyroid vein
The middle thyroid vein collects the blood from the lower part of the thyroid gland, and after being joined by some veins from the larynx and trachea, ends in the lower part of the internal jugular vein....

 and superior thyroid vein
Superior thyroid vein
The superior thyroid vein begins in the substance and on the surface of the thyroid gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein....


They form a plexus
A plexus is a part of nervous system. Plexus has a slightly different definition in vertebrates and in invertebrates.- In vertebrates :In vertebrates, a plexus is an area where nerves branch and rejoin. The electrical signals do not mix; rather, the fibres travel together with their electrical...

 in front of the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

, behind the Sternothyreoidei.

From this plexus, a left vein descends and joins the left innominate trunk, and a right vein passes obliquely downward and to the right across the innominate artery to open into the right innominate vein, just at its junction with the superior vena cava
Superior vena cava
The superior vena cava is truly superior, a large diameter, yet short, vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium...

; sometimes the right and left veins open by a common trunk in the latter situation.

These veins receive esophageal tracheal, and inferior laryngeal veins, and are provided with valves at their terminations in the innominate veins.
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