ANATOMY OF THE LARYNX 



485 



duction 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 laryn- 

 geal conveys to the brain the sensation which indicates the state of contraction of these 

 muscles. Both the branches co-operate 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 concave mirror round his head in such a manner that 



FIG. 346. The Parts of the Laryngoscope. 



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 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 



