116 



THE STUDY OF SPEECH CURVES. 



upward and outward (fig. 106). The form of the puff— sharp or smooth — 

 is determined by the way in which the glottal lips yield; the mode of 

 yielding depends on the way in which the separate fibers of the muscles 

 are contracted. When contracted along the medial edge (or edge of the 

 glottis) as indicated in figure 107, the action may approach that of a 

 stretched string loaded with a soft mass along its middle portion or along 

 its entire length. When contracted more laterally (figure 108), the action 

 may approach that of a soft mass flapping in a current of air, or of two soft 

 cushions striking together. These two forms of contraction correspond to 



Fig. 106— Method 

 of vibration at 

 the glottis. 



Fig. 107.— Glottal 

 lips with medial 

 loading. 



Fig. 108.— Glottal 

 lips with lateral 

 loading. 



separate action of the M. vocalis and the M. thyreoarytenoideus (externus). 

 ^^Tlen the slant fibers which insert along the medial edge of the glottal 

 lips (figure 109) are contracted, there will be nodal points similar to those 

 of stretched strings. 



These differences produce differences in the forms of the puffs. We 

 can thus explain the forms of puffs in the different types of vowels by 

 differences in the action of the muscles of the glottal lips. We may 

 assume that these muscles contract differently for the different vowels, 

 the vowel being formed at the glottis as well as in the mouth. This phe- 

 nomenon can be explained by supposing that certain sets of innervations 

 to the fibers of the glottal muscles as well as to the cavity muscles are 

 associated with the sound of each vowel. 



Physically stated, a vowel consists of a series of explosive puffs of 

 air from the glottis acting on a complicated cavity with considerable 

 friction. The puffs of air may be very brief and may be separated by 

 comparatively long intervals of rest; or they may be of smoother form. 



