542 



HANDBOOK OF PHYSIOLOGY. 



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

 and so alters 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 



.Lig.ary 



Cart. "Wrisbergii* 

 Cart. Santorint 



mm. Aryteu. obliqxt.' 



<. Crico-arytenoid. post,, 



Comu inferior 



"U-r. ceratorcric. 



Pars. post. inf. membrant 

 Pars, cartilag., 



Fig. 344. The larynx as seen from behind. To show the intrinsic muscles posteriorly. (Stoerk.) 



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 gently but firmly against the lower teeth by means of 

 a handkerchief. The warm mirror is passed to the back of the mouth, until 

 it rests upon and slightly raises the base of the uvula, and at the same time 

 the light is directed upon it : an inverted image of the larynx and trachea 

 will be seen in the mirror. If the dorsum of the tongue be alone seen, the 

 handle of the mirror must be slightly lowered until the larynx comes into 

 view ; care should be taken, however, not to move the mirror upon the uvula, 

 as it excites retching. The observation should not be prolonged, but should 

 rather be repeated at short intervals. 



The structures seen will vary somewhat according to the condition of the 

 parts as to inspiration, expiration, phonation, etc. ; they are (fig. 347) first, 

 and apparently at the posterior part, the base of the tongue, immediately below 

 which is the accurate outline of the epiglottis, with its cushion or tubercle. 

 Then are seen in the central line the true vocal cords, white and shining in their 

 normal condition. The cords approximate (in the inverted image) posteriorly ; 



