THE LARYXX. 1107 



tion of its antero-external 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 muscular process and outer border of the arytenoid cartilage above the 

 preceding fibres ; it lies on the outer side of the sacculus laryngis. 1 



The TJtyro-epiglottideus is a delicate fasciculus which arises from the angle of 

 the thyroid cartilage, close to the origin of the Thyro-arytenoid, and spreads out 

 upon the outer surface of the sacculus laryngis ; some of its fibres are lost in the 

 aryteno-epiglottic fold, whilst others pass to the margin of the epiglottis (Depressor 

 epiglottidis). 



The Aryteno-epiglottideus superior consists of a few delicate fasciculi, which 

 arise from the apex of the arytenoid cartilage and become lost in the aryteno-epi- 

 glottic fold. 



The Aryt: no-epiglottideus inferior (Compressor sacculi laryngis, Hilton), arises 

 from the arytenoid cartilage just below the preceding ; and passes forward and up- 

 ward, it spreads out upon the inner surface of the laryngeal pouch. 2 



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 Arvtenoideus 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 Cricn-arytfnoidt ! posti<-i 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 anterior angles and the ligaments attached to them become widely 

 separated, the vocal cords at the same time being made tense. 



The Grioo-arytaioidt i laterales close the glottis by rotating the arytenoid cartilages inward 

 so as to approximate their anterior angles. 



The Aryttitni'i]' /.* muscle* approximate the arytenoid cartilages, and thus close the opening 

 of the glottis, especially at its back part. 



The Crtco-thyroi'l un!.-les produce tension and elongation of the vocal cords. This is 

 effected as follows : the thyroid cartilage is fixed by the Thyro-hyoid muscles ; then the 

 Crico-thyroid muscles, when they act. draw upward the front of the cricoid cartilage, and so 

 depress the posterior portion, which carries with it the arytenoid cartilages, and thus elongate 

 the vocal o'.rils. 



The Tkyro-cerytauHdei muscles, consisting of two parts having different attachments and 

 different directions, are rather complicated as regards their action. Their main use is to draw 

 the ar.vte.noid cartilages forward toward the thyroid, and thus shorten and relax the vocal cords. 

 But. owing to the connection of the inner portion with the vocal cord, this part, if acting sep- 

 arately, is supposed to modify its elasticity and tension, and the outer portion, being inserted 

 into the outer part of the anterior surface of the arytenoid cartilage, may rotate it inward, and 

 thus narrow the rima elottidis by bringing the two cords together. 



The Thyro-qpiglottidei depress the epiglottis and assist in compressing the sacculi laryngis. 

 The Aryteno-epiglottideus superior constricts the superior aperture of the larynx, when it 

 is drawn upward, during deglutition, and the opening closed by the epiglottis. The Aryteno- 

 epiglottideus inferior, together with some fibres of the Thyro-arytenoidei, compress the sacculus 

 laryngis. 



The Mucous Membrane of the Larynx is continuous above with that lining the 

 mouth and pharynx, and is prolonged through the trachea and bronchi into the 

 lungs. It lines the posterior and upper part of the anterior surface of the epiglot- 

 tis, to which it is closely adherent, and forms the aryteno-epiglottic folds which 



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

 Internal thyro-arytenoid. 



: MuscTLfs TRiTiCEO-GLOssrs, Bochdalek. jun. (Prager VierteljaArssehrift, 2d part, 1866), 

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

 arises from the nodule of cartilage (corpus triticeum] in the posterior thyro-hyoid 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 

 ou one onlv. 



