ANATOMY OF THE LARYNX 515 



the muscles that close the glottis. Both these branches of the vagi cooperate 

 also in the production and regulation of the voice. The inferior laryngeal 

 determines the degree of contraction of the muscles that vary the tension of 

 the vocal cords, and the superior laryngeal conveys to the brain the sensation 

 which indicates the state of contraction of these muscles. Both the branches 

 cooperate also in the actions of the larynx in the ordinary slight dilatation and 

 contraction of the glottis in the acts of expiration and inspiration, more 

 evidently in the acts of coughing and other forcible respiratory movements. 



The Laryngoscope. This is an instrument employed in investigating the 

 condition of the pharynx, larynx, and trachea. It consists of a large concave 

 mirror with perforated center and of a smaller mirror fixed in a long handle. 

 In use the patient is placed in a chair, a good light (argand burner, or lamp) 

 is arranged on one side of, and a little above his head. The operator fixes the 



Lig. ary-epiglott. 



Cart. Wrisbergii. 

 Cart. Santorini. 



mm. Aryten. obliqu. 



m. Crico-arytenoid. post. 

 Cornu inferior. 

 Lig. cerato-cric. 



Pars. post, inf.membrani. 

 Pars, cartilag. 



FIG. 345. The Larynx as Seen from Behind. To show the intrinsic muscles posteriorly. 



(Stoerk.) 



concave mirror round his head in such a manner that he looks through the 

 central aperture with one eye. He then seats himself opposite the patient, 

 and so adjusts the position of the mirror, which is for this purpose provided 

 with a ball and socket joint, that a beam of light is reflected on the lips of the 

 patient. 



The patient is now directed to throw his head slightly backward, and to 

 open his mouth ; the reflection from the mirror lights up the cavity of the mouth, 

 and by a little alteration of the distance between the operator and the patient 

 the point at which the greatest amount of light is reflected by the mirror in 

 other words its focal length is readily discovered. The small mirror fixed 

 in the handle is then warmed, either by holding it over the lamp, or by putting 

 it into a vessel of warm water; this is necessary to prevent the condensation of 

 breath upon its surface. The degree of heat is regulated by applying the back 

 of the mirror to the hand or cheek, when it should feel warm without being 

 painful. 



After these preliminaries the patient is directed to put out his tongue, 

 which is held by the left hand of the operator gently but firmly against the 



