The internal laryngeal nerve springs from the superior laryngeal branch of the vagus. It is a sensory nerve, and its branches are distributed chiefly to the larynx, where it supplies the mucous membrane of the exterior, and also of the interior down to the vocal folds.

 

After piercing the thyrohyoid membrane, the internal laryngeal nerve sends filaments to the mucous membrane of the epiglottis and all its folds, and to the lower median part of the back of the tongue. It then supplies the mucous membrane that lines the side wall of the larynx and covers the side and back of the arytenoid cartilages and cricoid cartilage; and it communicates with the recurrent laryngeal nerve.

 

In the neck, the recurrent laryngeal nerve disappears, under cover of the lower border of the inferior constrictor muscle, and enters the larynx. It is the motor nerve of the larynx. It supplies all the muscles, with the exception of the cricothyroid, which obtains its nerve-supply from the external laryngeal. It contains a few sensory fibers also, and gives these to the lining mucous membrane of the larynx below the rima glottidis.

 

The recurrent laryngeal nerve, having entered the larynx, ascends on the side of the cricoid cartilage, immediately behind the cricothyroid joint, and communicates with a branch of the internal laryngeal nerve. One of its branches passes upward and backward under cover of the posterior cricoarytenoid muscle, supplying that muscle and the arytenoid muscles.

 

The superior laryngeal artery, a branch of the superior thyroid, accompanies the internal laryngeal nerve; the inferior laryngeal artery, which springs from the inferior thyroid, accompanies the recurrent nerve.