B. Muscles on the Inner Surface of the Cartilages of the Larynx.
M. thyreoarytenoideus ([Fig. 105], d).—The thyroarytenoid is a triangular, flat muscle of considerable size. It lies within the wing of the thyroid cartilage (2), and its fibres are nearly dorsoventral in direction.
Origin.—The median longitudinal crest on the dorsal surface of the thyroid cartilage (2).
Insertion.—The fibres converge to the insertion into the cranial lip of the laterocaudal angle of the arytenoid cartilage (4).
Action.—Turns the arytenoid on its oblique articulation so as to close the glottis.
M. cricoarytenoideus lateralis ([Fig. 105], c).—Triangular, a little smaller than the preceding, caudad of which it is situated, so that it also is covered by the wing of the thyroid.
Origin.—The lateral part of the cranial border of the cricoid cartilage (3). The fibres converge, passing dorsad.
Insertion.—The caudal lip of the laterocaudal angle of the arytenoid cartilage (4).
Action.—Similar to the preceding, so that it closes the glottis.