MUSCLES OF THE LARYNX. 489 



The Arytenoideus muscle occupies the posterior con- 

 ?ave surface of the arytenoid cartilages, between which 

 * is stretched. It consists of three planes of trans- 

 verse and oblique fibres ; hence it was formerly consi- 

 dered as several muscles, under the names of transversi 

 and obliqui. 



The three muscles of the epiglottis are the 



Thyro-epiglottideus, 

 Aryteno-epiglottideus superior, 

 Aryteno-epiglottideus inferior. 



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 and in the aryteno-epiglottidean fold of mucous membrane, in 

 which they are lost ; a few of the anterior fibres being continued onwards 

 to the side of the epiglottis. 



The Aryteno-epiglottideus superior consists of a few scattered fibres, 

 which pass forwards in the fold of mucous membrane forming 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, described by Mr. 

 Hilton, and closely connected with the sacculus laryngis, 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 arytenoid carti- 

 lage, just above the attachment of the chorda vocalis ; and passing for- 

 wards, 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. From a careful examination of the muscles of the larynx, Mr, 

 Bishopf concludes, that the crico-arytenoidei postici open the glottis, 

 while all the rest close it. The arytenoideus approximates the arytenoid 

 cartilages posteriorly, and the crico-arytenoidei laterales and thyro-aryte- 

 noidei anteriorly; the latter, moreover, close the glottis mesially. The 

 crico-thyroidei are tensors of the chorda? vocales, and these muscles, 

 together with the thyro-arytenoidei, regulate the tension, position, and 

 vibrating length of the vocal cords. 



The crico-thyroid muscles effect the tension of the chordae vocales by 

 rotating the cricoid on the inferior cornua of the thyroid ; by this action 

 the anterior portion is drawn upwards and made to approximate the infe- 

 rior border of the thyroid, while the posterior and superior border of the 

 cricoid, together with the arytenoid cartilages, is carried backwards. The 

 crico-arytenoidei postici separate the chordaB vocales by drawing the ary- 

 tenoid cartilages outwards and downwards. The crico-arytenoidei late- 

 rales, by drawing the outer angles of the arytenoid cartilages forwards, 

 approximate the anterior angles to which the chordae vocales are attached. 

 The thyro-arytenoidei draw the arytenoid cartilages forwards, and, by their 



* A side view of the larynx, one ala of the thyroid cartilage has been removed. 1. 

 The remaining ala of the thyroid cartilage. 2. One of the arytenoid cartilages. 3. One 

 of the cornicula laryngis. 4. The cricoid cartilage. 5. The crico-arytenoideus posticus 

 muscle. G. The crico-arytenoideus lateralis. 7. The thyro-arytenoideus. 8. The crico- 

 thyroidean membrane. 9. One half of the epiglottis. 10. The upper part of the trachea 



t Cyclopaedia of Anatomy and Physiology, art. Larynx 



