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MUSCLE-NERVE PHYSIOLOGY 



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 the following: first, and apparently 

 at the posterior part, the base of the tongue, immediately below which is the accurate out- 

 line of the epiglottis, with its cushion or tubercle, figure 348. Then are seen in the central 

 line the true vocal cords, white and shining in their normal condition. In the inverted image 

 the cords are closer together posteriorly. Between them is left an open slit, narrow while 

 a high note is being sounded, wide during a deep inspiration. On each side of the true 

 vocal cords, and on a higher level, are the false vocal cords. Still more externally than the 

 false vocal cords is the aryteno-epiglottidean fold, in which are situated upon each side 



FIG. 347. To Show the Position of the Operator and Patient when Using the Laryngoscope. 



three small elevations; of these the most external is the cartilage of Wrisberg, the interme- 

 diate is the cartilage of Santorini, while in front and somewhat below the preceding is the 

 summit of the arytenoid cartilage seen only during deep inspiration. The rings of the 

 trachea, and even the bifurcation of the trachea itself, if the patient be directed to draw 

 a deep breath, may be occasionally seen. 



Movements of the Vocal Cords. The position of the vocal cords in ordi- 

 nary tranquil breathing is so adapted by the muscles that the opening of the 

 glottis is wide and triangular, figure 348, B, becoming a little wider at each 

 inspiration, and a little narrower at each expiration. On making a rapid 

 and deep inspiration the opening of the glottis is widely dilated, figure 348, C, 

 and somewhat lozenge-shaped. 



In Vocalization. At the moment of the emission of a note the opening is 

 narrowed, the margins of the arytenoid cartilages being brought into contact 

 and the edges of the vocal cords approximated and made parallel at the same 

 time that their tension is much increased. The higher the note produced, the 

 tenser do the cords become, figure 348, A; and the range of a voice depends, of 

 course, in the main, on the extent to which the degree of tension of the vocal 

 cords can be thus altered. In the production of a high note the vocal cords 

 are brought well within sight, so as to be plainly visible with the help of the 

 laryngoscope. In the utterance of low tones, on the other hand, the epiglottis 



