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 Laryngeal Or Crico Thyroid Branch may come directly from the superior thyroid, but more usually it arises from its internal terminating branch. It passes horizontally inwards in front of the crico-thyroid membrane, and along the inferior margin of the thyroid cartilage, to anastomose with its fellow of the opposite side and supply the crico-thyroid membrane. This artery is pretty constant, though it varies as to size and origin. If it be absent at one side, the artery of the opposite side will be found larger than usual. It is often a branch of the superior laryngeal.
The internal terminating branch descends along the. internal margin of the corresponding lobe, and unites in forming an arch with the corresponding branch of the opposite side: this branch usually gives off the inferior laryngeal artery.
The external terminating branch descends along the external margin of the corresponding lobe, and anastomoses with the inferior thyroid.
The anterior terminating branch is distributed to the anterior surface of the upper portion of the gland: it is not always present.
Lastly, the posterior terminating branch descends between the front of the trachea and the thyroid gland, in the substance of which gland it is lost.
The superior thyroid artery lies on a plane anterior and internal to the common carotid; and, therefore, in attempts at suicide, it is the vessel usually divided. In this case, we may either secure the bleeding vessel, or put a ligature on the external carotid beneath the origin of the former. This artery has been tied for the purpose of reducing the size of a bronchocele, or preparatory to extirpating the thyroid gland. The incision that exposed the external carotid will also expose the origin of the superior thyroid. In a case related in Houston's Catalogue (p. 80), this vessel crossed the crico-thyroid membrane.