MUSCLES OF THE LARYNX. 483 



sists of three planes of transverse and oblique fibres ; hence it was 

 formerly considered as several muscles, under the names of trans- 

 versi and obliqui. 



The three muscles of the epiglottis are the 



Thyro-epiglottideus, 

 Aryteno-epiglottideus superior, 

 Aryteno-epiglottideus inferior (Hilton's muscle). 



The Thyro-epiglottideus appears to be formed by the upper fibres 

 of the thyro-arytenoideus muscle : they spread out upon the external 

 surface of the sacculus laryngis, on which they are lost; a few of 

 the anterior fibres being continued onwards to the side of the epi- 

 glottis. 



The Aryteno-epiglottideus superior consists of a few scattered 

 fibres, which pass forwards in the fold of mucous membrane form- 

 ing the lateral boundary of the entrance into the larynx, from the 

 apex of the arytenoid cartilage to the side of the epiglottis. 



The Aryteno-epiglottideus inferior. This muscle was discovered 

 by Mr. Hilton, and is very important in relation to the sacculus 

 laryngis, with which it is closely connected. It may be found by 

 raising the mucous membrane immediately above the ventricle of 

 the larynx. It arises by a narrow and fibrous origin from the ary- 

 tenoid cartilage, just above the attachment of the chorda vocalis ; 

 and passing forwards, and a little upwards, expands over the upper 

 half, or two-thirds of the sacculus laryngis, and is inserted by a 

 broad attachment into the side of the epiglottis. 



Actions. The crico-thyroid and arytenoid muscles are contractors 

 of the rima glottidis ; the crico-arytenoideus posticus and lateralis, 

 and the thyro-arytenoideus, are dilators. 



The crico-thyroid muscles elongate, and thereby bring together 

 the chordae vocales, by drawing the thyroid cartilage downwards 

 and forwards ; their posterior attachment at the arytenoid cartilages 

 being fixed. The arytenoid muscle approximates the arytenoid 

 cartilages, and consequently the chorda vocales, directly. The 

 crico-thyroidei postici being attached to the outer angles of the 

 bases of the arytenoid cartilages, draw them from each other, and 

 stretch the chordae vocales. The crico-arytenoidei laterales draw 

 the arytenoid cartilages from each other, -but relax the chordae vo- 

 cales ; and the thyro-arytenoidei increase the width of the glottis, 

 by directly relaxing the chordae vocales. 



The thyro-epiglottideus acts principally by compressing the glands 

 of the sacculus laryngis and the sac itself: by its attachment to the 

 epiglottis it would act feebly upon that valve. The aryteno-epiglot- 

 tideus superior serves to keep the mucous membrane of the sides of 

 the opening of the glottis tense, when the larynx is drawn upwards, 

 and the opening closed by the epiglottis. Of the aryteno-epiglotti- 

 deus, the " functions appear to be," writes Mr. Hilton, " to compress 

 the subjacent glands which open into the pouch ; to diminish the 



