THE LARYNX. 963 



fibres pass backward and outward, to be inserted into the base and anterior surface 

 of the arytenoid cartilage. This muscle consists of two fasciculi. 1 The inner or 

 inferior portion, the thicker, is inserted into the vocal process of the arytenoid 

 cartilage, and into the adjacent portion of its anterior surface; it lies parallel with 

 the true vocal cord, to which it is adherent. The outer or superior fasciculus, the 

 thinner, is inserted into the anterior surface and outer border of the arytenoid 

 cartilage above the preceding fibres ; it lies on the outer side of the sacculus 

 laryngis, immediately beneath the mucous membrane. 2 

 The muscles of the epiglottis are the 



Thyro-epiglottideus. Aryteno-epiglottideus superior. 



Aryteno-epiglottideus inferior. 



The Tltyro-epiglottideus is a delicate fasciculus, which arises from the inner 

 surface of the thyroid cartilage, just external to the origin of the Thyro-arytenoid 

 muscle, of which it is sometimes described as a part, and spreads over the outer 

 surface of the sacculus laryngis ; some of its fibres are lost in the aryteno-epiglot- 

 tidean fold, while the others are continued forward to the margin of the epiglottis 

 (Depressor epiglottidis). 



The Aryteno-epiglottideus superior consists of a few delicate muscular fascic- 

 uli, which arise from the apex of the arytenoid cartilages, and become lost in the 

 fold of mucous membrane extending between the arytenoid cartilage and the side 

 of the epiglottis (aryteno-epiglottidean fold). 



The Aryteno-epiglottideus inferior (Compressor sacculi laryngis, Hilton) arises 

 from the arytenoid cartilage, just above the attachment of the superior vocal cord ; 

 passing forward and upward, it spreads out upon the anterior surface of the epi- 

 glottis. This muscle is separated from the preceding by an indistinct areolar 

 interval. 3 



Actions. In considering the action of the muscles of the larynx, they may 

 be conveniently divided into two groups, viz.: 1. Those which open and close 

 the glottis. 2. Those which regulate the degree of tension of the vocal cords. 



1. The muscles which open the glottis are the Crico-arytenoidei postici ; and 

 those which close it are the Arytenoideus and the Crico-arytenoidei laterales. 

 2. The muscles which regulate the tension of the vocal cords are the Crico- 

 thyroidei, which tense and elongate them ; and the Thyro-arytenoidei, which relax 

 and shorten them. The Thyro-epiglottideus is a depressor of the epiglottis, and 

 the Aryteno-epiglottidei constrict the superior aperture of the larynx, compress 

 the sacculi laryngis, and empty them of their contents. 



The Ci'ico-arytenoldel. postici separate the chordae vocales, and consequently open the glottis, 

 by rotating the arytenoid cartilages outward around a vertical axis passing through the crico- 

 arytenoid joints, so that their vocal processes and the vocal cords attached to them become widely 

 separated. 



The Orico-cvrytenoidei laterales close the glottis by rotating the arytenoid cartilages inward 

 so as to approximate their vocal processes. 



The Arytenoideus muscles approximate the arytenoid cartilages, and thus close the opening 

 of the glottis, especially at its back part. 



The Orieo-tkyroid muscles produce tension and elongation of the vocal cords. This is 

 effected as follows : the thyroid cartilage is fixed by its extrinsic muscles ; then the Crico- 

 thyroid muscles, when they act, draw upward the front of the cricoid cartilage, and so depress 



1 Henle describes these two portions as separate muscles, under the names of External and 

 Internal thyro-arytenoid. 



' 2 Luschka has described a small but fairly constant muscle as the Arytenoideus rectus. It is 

 attached below to the posterior concave surface of the arytenoid cartilage, beneath the Arytenoideus 

 muscle, and, passing upward, emerges at the upper border of this muscle, and is inserted into the 

 posterior surface of the cartilage of Santorini (Anatomy, by Hyrtl, page 718). 



3 MUSCULUS TIUTICECM;I,OSSUS. Bochdalek, jun. (Prager Vierteljahrsschrift, 2d part, 1866), 

 describes a muscle hitherto entirely overlooked, except a brief statement in Henle's Anatomy, which 

 arises from the nodule of cartilage (corpus triticeum) in the posterior thyro-hvoid ligament, and passes 

 forward and upward to enter the tongue along with the Hyo-glossus muscle. He met with this 

 muscle eight times in twenty-two subjects. It occurred in both sexes, sometimes on both sides, at 

 others on one only. 



