352 



PULMONARY MUCOUS TISSUE. 



posterior crico-arytenoid ; the second action is produced by 

 the contraction of the muscle which forms the base of the 

 triangle of the glottis, the ary-arytenoid muscle, which dis- 

 places all the arytenoid cartilages, and makes them slide in- 

 wards (Fig. 91). 



Fig. 91. Entire obliteration of the aperture of the glottis.* 



All modifications in the form of the glottis are owing to 

 these two kinds of movement : the rocking movement^ and 

 movement of displacement of the whole box ; the two ex- 

 treme fjrms of the glottis thus produced are the lozenge 

 shape, which appears during inspiration, and the linear form, 

 to which a tendency is shown during expiration (see Respir- 

 ation, p. 302) : this is, however, more especially connected 

 with phonation and straining : this explains why we often 

 hear a sound, or peculiar cry, uttered by a person who is 

 making any great effort. We also see that one only of the 

 four intrinsic or interior muscles of the larynx serves to dilate 

 the glottis : this is the posterior crico-arytenoid ; the lateral 

 crico-arytenoid and the ary-arytenoid serve to obliterate it, 

 and reduce it to the condition of a chink. We must also 

 observe that the contraction of the thyro-arytenoid muscle, 

 which is situated in the thickest part of the glottis, like all 

 curved muscles placed around an aperture, completes its 



* Action of the arytenoid muscles, median movement of the arytenoid car- 

 tilages, in the direction indicated by the two arrows. The dotted lines indicate 

 the new position of the arytenoids and the new form of the glottis. (L. Maudl.) 



