962 



THE ORGANS OF VOICE AND RESPIRATION. 



The inner borders of these two muscles are separated in the middle line by a 

 triangular interval occupied by the central part of the crico-thyroid membrane. 



The Orico-arytenoideus posticus arises from the broad depression occupying 

 each lateral half of the posterior surface of the cricoid cartilage ; its fibres pass 

 upward and outward, converging to be inserted into the outer angle (muscular proc- 

 ess) of the base of the arytenoid cartilage. The upper fibres are nearly hori- 

 zontal, the middle oblique, and the lower almost vertical. 1 



The Grico-arytenoideus lateralis is smaller than the preceding, and of an 

 oblong form. It arises from the upper border of the side of the cricoid cartilage, 

 and, passing obliquely upward and backward, is inserted into the muscular process 

 of the arytenoid cartilage in front of the preceding muscle. 



The Arytenoideus is a single muscle filling up the posterior concave surface 

 of the arytenoid cartilages. It arises from the posterior surface and outer border 



of one arytenoid cartilage, and is in- 

 serted into the corresponding parts of 

 the opposite cartilage. It consists of 

 three planes of fibres, two oblique and 

 one transverse. The oblique fibres, 

 the most superficial, form two fasciculi, 



Cornicula 

 laryngis. 



Articular facet for 

 inferior comu of 

 thyroid cartilage. 



FIG. 531. Muscles of larynx, 

 of thyroid cartilage removed. 



Side view. Right ala 



FIG. 532. Interior of the larynx, seen from above. 

 (Enlarged.) 



which pass from the base of one cartilage to the apex of the opposite one. The 

 transverse fibres, the deepest and most numerous, pass transversely across between 

 the two cartilages ; hence the Arytenoideus was formerly considered as three mus- 

 cles, the transverse and the two oblique. A few of the oblique fibres are occa- 

 sionally continued round the outer margin of the cartilage, and blend with the 

 Thyro-arytenoid or the Aryteno-epiglottideus muscle. 



The Thyro-arytenoideus is a broad, flat muscle, which lies parallel with the 

 outer side of the true vocal cord. It arises in front from the lower half of the 

 receding angle of the thyroid cartilage, and from the crico-thyroid membrane. Its 



1 Merkel, of Leipsic, has described a muscular slip which occasionally extends between the outer 

 border of the posterior surface of the cricoid cartilage and the posterior margin of the inferior cornu 

 of the thyroid; this he calls the " Musculus kerato-cricoideus." It is not found in every larynx, 

 and when present exists usually only on one side, but is occasionally found on both sides. " Sir Wil- 

 liam Turner (Edinburgh Medical Journal, Feb., 1860) states that it is found in about one case in five. 

 Its action is to fix the lower horn of the thyroid cartilage backward and downward, opposing in some 

 measure the part of the Crico-thyroid muscle, which is connected to the anterior margin of the horn. 



