This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Inferior Thyroid Artery first ascends a little, and then turns inwards behind the internal jugular vein, pneumogastric nerve, and carotid artery; towards all of which parts it presents a slight concavity; its convexity being turned backwards towards the vertebral artery, which it consequently separates from the carotid. The trunk of the sympathetic nerve usually descends on the front of this vessel, forming on the right side a small ganglion, the middle cervical, which lies on the anterior surface of the artery: in other, but rare cases, the sympathetic nerve descends behind it. As the inferior thyroid artery approaches the thyroid gland, it forms another slight curve, the concavity of which looks backwards and corresponds to the recurrent nerve, which a little farther on passes between its terminating branches, particularly on the right side : on the left side we find that, in addition to the preceding relations, the inferior thyroid artery lies on the oesophagus, and is intimately connected with the thoracic duct, which usually lies behind it in the first instance, and then makes an arch to terminate in the left subclavian vein in front of the artery. The branches of the inferior thyroid artery are classed into the inferior, superior, and terminating. The Inferior branches are variable in number; they descend into the chest, supply the oesophagus, longus colli muscle, bronchial tubes and glands, and anastomose with the superior intercostal and bronchial arteries. The Superior branches are distributed to the longus colli and anterior scalenus muscles: one of these is constant, and, though usually small, is sometimes of considerable size; it is termed the ascendens colli; it ascends on the front of the scalenus anticus muscle, parallel and internal to the phrenic nerve. Its branches are distributed to the muscles on the front of the vertebral column; some of them inosculate with descending branches of the occipital artery, and others penetrate the lateral foramina of the spine to communicate with branches of the vertebral. The ascendens colli often comes off directly from the thyroid axis, and is frequently so described. The Terminating branches of the inferior thyroid artery enter into the inferior and posterior portion of the thyroid gland, anastomose with the terminating branches of the superior thyroid, and are lost in the substance of the gland.
The operations of tying one or more of the thyroid arteries has been performed with a view to diminish the size of a bronchocele, or previously to extirpation of the thyroid gland. The inferior thyroid artery may be exposed by laying bare the sheath of the carotid artery in the manner already recommended, and drawing it to the external side: when this has been done, the inferior thyroid artery may be discovered crossing inwards, opposite, in most cases, to the fifth cervical vertebra; and care will be necessary to avoid the recurrent and sympathetic nerves on both sides, and the thoracic duct on the left side.
The inferior thyroid artery of the left side is particularly engaged in performing the operations of cesopha-gotomy.