776 ORGANS OF VOICE AND RESPIRATION. 



outer surface of the sacculus laryngis, some of its fibres are lost in the aryteno- 

 epiglottidean fold, whilst others are continued forwards to the margin of the 

 epiglottis (Depressor Epiglottidis). 



The Arytseno-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 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-arytsenoidei Postici ; and 

 those which close it, are the Arytaenoideus, and the Crico-arytaanoidei Laterales. 

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

 thyroidei, which tense and elongate them; and the Thyro-arytasnoidei, which 

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

 and the Arytasno-epiglottidei constrict the superior aperture of the larynx, 

 compress 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 arytenoid cartilages, and thus closes the opening 

 of the glottis, especially at its back part. 



The Crico-thyroid muscles produce 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 1 assist in compressing the sacculi laryngis. 

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

 drawn upwards, during deglutition, and the opening closed by the epiglottis. The Arytaeno- 

 epiglottideus 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 adhe- 

 rent, 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 reduplication, the chief part of the superior, or false, vocal cord ; and, 

 from the ventricle, 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 surface of the crico-thyroid membrane, and cricoid cartilage ; and is 

 ultimately continuous 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. 



Glands. The mucous membrane of the larynx is furnished with numerous 

 muciparous glands, the orifices of which are found in nearly every part : they 

 are very numerous upon the epiglottis, being lodged in little pits in its sub- 

 stance ; they are also found in large numbers along the posterior margin of the 

 aryteno-epiglottidean fold, in front of the arytenoid cartilages, where they are 



