212 



ADVANCED PHYSIOLOGY 



cle 



triangular opening for air to go through in ordinary breathing. 

 The straight inner borders of these membranes next to the 

 triangular passages form the vocal cords. 



Sound and Voice. In making a sound the vocal cords are 

 drawn very near one another at their posterior ends, and are 



stretched tightly; air is then 

 forced through the slit between 

 them. In this stretching oi 

 the cords several muscles are 

 concerned. In Figure 106 the 

 muscles marked A and B open 

 and close the space between 

 the vocal cords by moving the 

 arytenoid cartilages to which 

 they are attached. The muscle 

 marked C will evidently loosen 

 the cords. One of the muscles 

 that tightens them is shown 

 in the figure at D. 



Essentially this same mech- 

 anism for voice production is 

 present in many lower animals, 

 e.g. frogs and toads, dogs, 

 sheep, seals, etc. The song of 

 birds is produced by a somewhat different structure. 



Since sound is due to extremely rapid movements in the air, 

 how can the vocal cords be set in vibration when the air coming 

 from the lungs is passing them in a continuous and steady cur- 

 rent? The expiratory muscles, i.e. those of the ribs and 

 abdomen, certainly do not go through 2000 contractions per 

 second, and thus send air from the lungs in as many little 

 "puffs"; yet 2000 per second is the rate of vibration in the air 

 which is required to produce some of the higher tones a person 

 can sing. We all do know, however, that a blade of grass 

 or a strip of paper drawn between the lips will vibrate very 



Vocal Cords 



FlG. 106. T HE LARYNX AS 



VIEWED FROM ABOVE 

 A part of the membranes and muscles 

 are removed so as to show the chief 

 muscles concerned in opening and 

 closing (Muscles A and B) as well as 

 those that loosen (Muscle C) the vocal 

 cords. Muscle D is one of those which 

 tighten the cords. (Carter) 



