270 A MANUAL OF PHYSIOLOGY 



Rolando, in the macaque monkey, causes adduction of the 

 vocal cords, never abduction. Stimulation of the medulla 

 oblongata (accessory nucleus) causes abduction, never adduc- 

 tion (Horsley and Semon). 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 ; for Hooper has found that 

 in an animal deeply narcotized with ether, stimulation of 

 the recurrent laryngeal nerve causes invariably abduction of 

 the vocal cords ; in an animal slightly narcotized, adduction. 

 On the other hand, 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 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 of the crico-thyroid muscle and 

 increased tension of the cords. Section or paralysis of the 

 inferior laryngeal nerves leads to loss of voice or aphonia, 

 and dyspnoea (Fig. 99). Both adductor and abductor 

 muscles are paralyzed ; the vocal cords assume their mean 

 position the position they have in the dead body and the 

 glottis can neither be narrowed to allow of the production 

 of a note, nor widened during inspiration. It is said, how- 

 ever, that young animals, in which the structures around the 

 glottis are more yielding than in adults, can still utter shrill 

 cries after section of the inferior laryngeals, the contraction 

 of the crico-thyroid muscle alone being able, while increasing 

 the tension of the cords, to draw them together. Strong 



