THE THYROID GLAND:
Netter Plate Number: 68A

The thyroid gland produces a hormone thyroxin, stored in the follicles, and released accordingly to control the metabolic rate of the body. This gland is composed of two lateral lobes which is connected midline by the isthmus. A pyramidal lobe is present approximately 50% of the time, usually noted on the left side.
The thyroid gland is attached to the trachea by Berry's ligament.

The blood supply of this endocrine organ is rich. The thyroid arteries include the:
superior thyroid artery, which is usually the first branch of the external carotid artery, and the
inferior thyroid artery, a branch of the thyrocervical trunk of the subclavian artery. This artery is unique in that it travels independently of venous structures This artery ascends along the medial border of the anterior scalene muscle behind the carotid sheath and sympathetic trunk.
The thyroidea ima artery is present around 4-10% of the time, and ascends from the brachiocephalic artery or directly from the aorta. It ascends along the ventral surface of the trachea.

The venous return consists of the superior, middle and inferior thyroid veins.
The superior thyroid vein crosses the common carotid artery to empty into the internal jugular vein, and is the only thryoid vein to accompany an artery.
The middle thyroid vein also crosses the common carotid to empty into the internal jugular.
The inferior thyroid vein descend along the trachea to empty into the brachiocephalic veins.

The recurrent laryngeal nerves, with esophageal, tracheal, cardiac, pharyngeal branches in addition to giving off the inferior laryngeal nerve both arise from the vagal nerves before their ascent into the larynx.
The right recurrent laryngeal nerve loops inferiorly around the subclavian artery to ascend between the trachea and esophagus.
The left recurrent laryngeal nerve loops inferiorly around the aorta, and ascends, maintaining a course more closely related to the trachea.