PHONATION; ARTICULATE SPEECH. 629 



Laryngoscopic examination of the larynx in the human being shows that 

 during quiet respiration the vocal bands are widely separated and almost 

 stationary, moving but slightly during either inspiration or expiration. At 

 this time, according to the investigations of Semon, the area of the glottis is 

 approximately 160 sq. mm., somewhat less than the area of either the 

 supraglottic or infraglottic regions, which is about 200 sq. mm. This con- 

 dition of the glottis is maintained by the steady continuous contraction of the 

 posterior crico-ary tenoid muscles, the abductors of the vocal bands. 



For phonatory purposes it is essential that the respiratory function be 

 temporarily suspended and the vocal bands closely approximated. This is 

 accomplished by the contraction of the remaining muscles of the larynx, 

 with the exception of the crico-thyroid, which are collectively known as the 

 adductors of the vocal bands. During phonation the adductor muscles over- 

 come the activity of the abductors. With the cessation of phonation the 

 abductors immediately restore the vocal bands to their former respiratory 

 position. 



The activities of these two a-ntagonistic groups of muscles are under the 

 control of the central nerve system. The only pathway for the excitator 

 nerve impulses is through the fibers of the inferior or recurrent laryngeal 

 nerve. The relation of these nerve-fibers both centrally and peripherally, as 

 well as their physiologic action, has been the subject of much experimenta- 

 tion. The results have not always been in accord, owing to the choice of 

 animal, the use of anesthetics, strength of stimulus, etc. 



As the outcome of many investigations it is believed that each muscle 

 group is innervated by its own bundle of nerve-fibers, both of which are con- 

 tained in the inferior laryngeal, though coming from two separate centers in 

 the medulla oblongata. Russell succeeded in separating the fibers for the 

 abductors from the fibers for the adductors in the inferior laryngeal, and in 

 tracing them to their terminations. So completely was this done that it 

 became possible to produce at will, through stimulation, either abduction 

 or adduction, without contraction of the muscle of opposite function. 



The laryngeal respiratory center was located by Semon and Horsley, 

 in the cat, in the upper part of the floor of the fourth ventricle. Stimulation 

 of this area during etherization was followed by abduction of the vocal 

 bands. The efferent fibers of this center are believed by some investigators 

 to leave the central nerve system in the spinal accessory nerve, by others in 

 the lower roots of the vagus. 



From the continuous activity of the abductor muscle, and the stationary 

 position of the vocal bands, it is probable that the medullary center is in a 

 state of continuous activity or tonus, the result probably of reflex influences. 



A cortical representation for laryngeal respiratory movements has been 

 determined by Semon and Horsley in different classes of animals. In the 

 cat especially, stimulation of the border of the olfactory sulcus gives rise to 

 complete abduction of the vocal bands on both sides. The representation is 

 therefore bilateral. 



The phonatory center was located by the same investigators in the medulla 

 near the ala cinerea and the upper border of the calamus scriptorius. Stimu- 

 lation of this area was invariably followed by bilateral adduction of the vocal 

 bands and closure of the glottis. 



