THE ORGANS OF SENSE. 



149 



Hyoid bone. 



Thyro-arytas 

 noideus muscle. 



membrane above the level of the -glottis are covered by stratified 

 squamous epithelium. 



The glottis is opened by the posterior crico-arytenoid muscles, which 

 by their contraction rotate the arytenoid cartilages on their vertical 

 axis in such a way that the vocal processes are turned outwards. 

 Rotation of these cartilages in the reverse direction is effected by 

 the lateral crico-arytenoid 

 muscles, contraction of 

 which approximates the 

 vocal cords. The closure 

 of the glottis is assisted 

 by the contraction of the 

 arytenoid muscles, which, 

 by approximating the aryte- 

 noid cartilages, bring to- 

 gether the posterior ends 

 of the vocal cords. The 

 crico-thyroid muscles by 

 their contraction cause the 

 cricoid to rotate on the 

 thyroid cartilage, so that 

 the broad part of the former 

 is drawn downwards and 

 backwards and the vocal 

 cords are made tense. The 

 general action of the thyro- 

 arytenoid muscles is to draw 

 the arytenoid cartilages to- 

 wards the anterior part of 



the thyroid and so relax ~ 



FIG. 4/. Coronal section of larynx and upper part 



the vocal cords. of trachea. (Gray's Anatomy.} 



The movements which 



occur in the larynx in connection with swallowing and breathing will 

 be referred to in the descriptions of deglutition and respiration. The 

 changes which occur in the larynx during voice production are observed 

 with the aid of the laryngoscope. This instrument consists of a mirror 

 which can be held in position in the pharynx so as to give a reflected 

 image of the interior of the larynx to the eye of the observer. In such 

 an image the vocal cords appear white, the false vocal cords more pink 

 in colour. 



When a note is produced the vocal cords are brought close together, 

 and an expiratory current of air causes them to vibrate. The current 



