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 Superior Thyroid Artery arises opposite the thyro-hyoid space. It first ascends towards the os hyoides, and then descends on the side of the larynx on a plane anterior and internal to the external carotid, to terminate in the thyroid gland. In this course it describes a curvature, the convexity of which looks upwards, touches the os hyoides, and corresponds to the concavity of a similar curvature in the lingual artery. Posteriorly it rests on some areolar tissue and the superior laryngeal nerve: anteriorly it is covered by the integuments, platysma myoides, cervical fascia, and by some small veins passing outwards from the larynx to the internal jugular vein; also by the sterno-hyoid, sternothyroid, and omo-hyoid muscles, and an internal branch of the descendens noni nerve which supplies the latter muscle.
The superior thyroid artery gives off the following branches:—
Superior Laryngeal. Inferior Laryngeal or Crico-Thyroid. Terminating.
The Hyoidean Branch, which is small, passes inwards beneath the thyro-hyoid muscle, supplies the areolar tissue in this situation, and anastomoses with the corresponding branch of the opposite side.
The Superior Laryngeal Branch descends with the superior laryngeal nerve, passes beneath the thyro-hyoid muscle, and pierces the ligament of the same name. Here it divides into two branches,—one of which ascends behind the os hyoides to supply the anterior surface of the epiglottis and mucous membrane: the other descends on the inside of the ala of the thyroid cartilage, and terminates in the crico-arytenoid and crico-thyroid muscle, and by a great number of small branches in the mucous membrane of the larynx.
The Sterno Mastoid Branch is constant, but variable in size: it crosses in front of the sheath of the carotid artery to reach the deep surface of the sterno-mastoid muscle, in which it is lost. This artery frequently arises from the posterior part of the external carotid, close to the origin of the lingual ; from this point it first runs upwards, hooks over the lingual nerve, which it draws into an angle salient downwards; and then, running downwards and outwards, it reaches the deep-seated surface of the sterno-mastoid.