286 A MANUAL OF PHYSIOLOGY 



ascending frontal convolution, near the fissure of Rolando, in 

 the macaque monkey, causes adduction of the vocal cords, never 

 abduction. In the cat, 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 important, 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 



FIG. 127. DIAGRAM OF VOCAL CORDS IN PARALYSES OF THE LARYNX. 



a, Paralysis of both inferior laryngeal nerves. The voca.1 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 ' 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. 



excited through the inferior laryngeal nerve. Thus, strong 

 stimulation of the inferior laryngeal causes closure of the glottis, 

 for although it supplies both abductors 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 

 adductors. The same is true when it is allowed to become dry. 

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

 posterior crico-arytenoid, an abductor muscle, was the first of 

 the intrinsic laryngeal muscles to lose its excitability. Lesions 

 of the medulla oblongata are pften 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 



