A. Muscles on the Outer Surface of the Larynx.
M. cricothyreoideus ([Fig. 96], n).—A broad flat band which with its fellow covers the ventral surface of the cricoid cartilage and the cricothyroid ligament.
Origin.—The lateral half of the ventral surface of the cricoid cartilage. The muscles diverge so as to leave a part of the cricothyroid ligament between them.
Insertion.—The ventral part of the caudal border of the thyroid cartilage laterad of the median ventral notch.
M. cricoarytenoideus posterior ([Fig. 105], b).—The two muscles cover the dorsal surface of the larynx.
Origin.—From the dorsal part of the caudal border of the cricoid cartilage (3) and from its median dorsal crest. The fibres pass craniolaterad, converging. The lateral fibres are nearly longitudinal in direction.
Insertion.—The dorsal border of the caudal end of the arytenoid cartilage (4).
Action.—Moves the arytenoid on its oblique articulation with the thyroid. The apex of the arytenoid is thus carried laterad, and the vocal cords are separated so as to widen the glottis.
Fig. 105.—Muscles of the Larynx, as Exposed by Removal of most of the Left Half of the Thyroid Cartilage.