_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. [Illustration: FIG. 105.--MUSCLES OF THE LARYNX, AS EXPOSED BY REMOVAL OF MOST OF THE LEFT HALF OF THE THYROID CARTILAGE. 1, epiglottis; 2, portion of the thyroid cartilage (cut); 3, cricoid cartilage; 4, arytenoid cartilage; 5, trachea. _a_, M. arytenoideus transversus; _b_, M. cricoarytenoideus posterior; _c_, M. cricoarytenoideus lateralis; _d_, M. thyreoarytenoideus.] =M. arytenoideus transversus= (Fig. 105, _a_).--A small unpaired muscle running transversely between the caudal ends of the arytenoid cartilages, just beneath the mucous membrane and parallel to the cranial border of the cricoid cartilage. =M. glossoepiglotticus.=--A small longitudinal muscle, lying by the side of its fellow in the frenulum of the epiglottis. _Origin._--The median fibrous septum of the tongue. _Insertion._--The dorsal (cranial) surface of the epiglottic cartilage in the median line near its attached border. _Action._--Draws the epiglottis craniad. =M. hyoepiglotticus= is a small bundle of parallel fibres lying in the frenulum of the epiglottis craniad and dorsad of the body of the hyoid bone. _Origin._--The lateral end of the cranial surface of the body of the hyoid. The two muscles pass craniodorsad, converging, and unite with the preceding. _Insertion_ with the preceding. (The lateral portion of the muscle may continue craniad to the tongue as a second part of the hyoglossus.) _Action._--Like the preceding. 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.