3*6 VOICE AN'D SPEECH 



abduction. In the eat, however, abduction of the cords may also 

 be obtained by stimulation of the cortex. The same is true of the 

 dog, but only when the peripheral adductor nerves have been 

 divided. Stimulation of the medulla oblongata (accessory nucleus) 

 causes abduction, never adduction. The skilled adductor function 

 is, therefore, placed under control of the cortex. The vitally im- 

 portant, but more mechanical, abductor function is governed by 

 the medulla. The abductor movements are more likely to be 

 affected by organic disease, the adductor movements by functional 

 changes. But the distinction between the two groups of muscles 

 is not entirely due to a difference of central connections, since by 

 altering the strength of the stimulus and the external conditions 

 the one or the other may be separately excited through the inferior 

 laryngeal nerve. Thus, strong stimulation of the inferior laryngeal 

 causes closure of the glottis, for although it supplies both abductors 



III 



Fig. 149. Diagram of Vocal Cords in Paralyses of the Larynx, a, Paralysis of both 

 inferior laryngeal nerves. The vocal cords have taken up the ' mean ' position. 

 b. Paralysis of right inferior laryngeal nerve. An attempt is being made to 

 narrow the glottis for the utterance of sound. The right cord remains in its 

 5 mean ' position, 'c. Paralysis of the abductor muscles only, on both sides. The 

 cords are approximated beyond the ' mean ' position by the action of the 

 adductors. 



and adductors, the latter, as the stronger muscles, prevail. With 

 weak stimulation, and in young animals, the abductors, owing to 

 the greater excitability of the neuro-muscular apparatus, carry off 

 the victory, and the glottis is opened (Russell). 



When the nerve is cooled the abductors give way before the 

 adductor;. The same is true when it is allowed to become dry. 

 And after death in a cholera patient it was observed that the pos- 

 terior cric.o-arytenoid, an abductor muscle, was the first of the 

 intrinsic laryngeal muscles to lose its excitability. Lesions of the 

 medulla oblongata are often accompanied by marked changes in 

 the character of the voice and the power of articulation. 



Section or paralysis of the superior laryngeal nerve causes the 

 voice to become hoarse, and renders the sounding of high notes an 

 impossibility, owing to the want of power to make the vocal cords 

 tense. Stimulation of the vagus within the skull causes contraction 



