710 ORGANS OF VOICE AND RESPIRATION. 



The muscles of the epiglottis are the 



Thyro-epiglottideus. 

 Arytseno-epiglottideus superior. 

 Arytaeno-epiglottideus inferior. 



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

 of the thyroid cartilage, just external to the origin of the Thyro-ary tenoid muscle, 

 and. spreading out upon the outer surface of the sacculus laryngis, some of its 

 fibres are lost in the aryteno-epiglottidean fold, whilst others are continued for- 

 wards to the margin of the epiglottis (Depressor epiglottidis). 



The Arytaeno-epiglottideus superior consists of a few delicate muscular fasciculi, 

 which arise from the apex of the arytenoid cartilage, and become lost in the fold 

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

 epiglottis (aryteno-epiglottidean folds). 



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

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

 passing forwards and upwards, it spreads out upon the inner and upper part of 

 the sacculus laryngis, and is inserted, by a broad attachment, into the margin of the 

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

 interval. 



Actions. In considering the actions 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-arytasnoidei postici ; and 

 those which close it are the Arytcenoideus, and the Crico-arytasnoidei laterales. 

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

 thyroidei, which make tense and elongate them, and the Thyro-aryta3noidei, which 

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

 and the Aryta3no-epiglottidei constrict the superior aperture of the larynx, com- 

 press the sacculi laryngis, and empty them of their contents. 



The Crico-arytcenoidei postici separate the chordae vocales, and, consequently, open the glottis, 

 by rotating the base of the arytenoid cartilages outwards and backwards ; 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 Crico-arytcenoidei laterales close the glottis, by rotating the base of the arytenoid carti- 

 lages inwards, so as to approximate their anterior angles. 



The Arytcenoideus muscle approximates the aryteuoid cartilages, and thus closes the opening 

 of the glottis, especially at its back part. 



The Crico-thyroid muscles effect the tension and elongation of the vocal cords, by drawing 

 down the thyroid cartilage over the cricoid. 



The Thyro-arytcenoidei muscles draw the arytenoid cartilages, together with the part of the 

 cricoid to which they are connected, forwards towards the thyroid, and thus shorten and relax 

 the vocal cords. 



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

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

 drawn upwards, during deglutition, and the opening closed by the epiglottis. The Aryice.no- 

 cpiglottideus inferior, together with some fibres of the Thyro-arytaenoidei, 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 both surfaces of the epiglottis, to which it is closely adherent, 

 and forms the aryteno-epiglottidean folds, which encircle the superior aperture of 

 the larynx. It lines the whole of the cavity of the larynx ; forms, by its redu- 

 plication, the chief part of the superior or false vocal cord ; and, from the ven- 

 tricle, is continued into the sacculus laryngis. It is then reflected over the true 

 vocal cords, where it is thin, and very intimately adherent, covers the inner sur- 

 face of the crico-thyroid membrane, and cricoid cartilage, and is ultimately con- 

 tinuous with the lining membrane of the trachea. It is covered with columnar 

 ciliated epithelium, below the superior vocal cord ; but, above this point, the cilise 

 are found only in front, as high as the middle of the epiglottis. In the rest of its 

 extent, the epithelium is of the squamous variety. 



