572 PHYSIOLOGY. 



The principal change in form consists in the lengthening and short- 

 ening of the mouth. The vowels are a, e, i, o, and u. 



The consonants consist of sounds emitted by the larynx, but 

 which become noises by reason of obstacles they encounter. Accord- 

 ing to the obstructions met with, consonants are termed gutterals 

 (h, ~k, q), linguals (c, d, g, t, s, n, I, r), and labials (b, f, m, p, v). The 

 linguals are subdivided into palatals and dentals. 



The very varied union of the vowels with the consonants con- 

 stitutes syllables; union of the latter forms words. 



Stammering is due to a continued spasmodic contraction of the 

 diaphragm a'nd to the muscles of the larynx not harmonizing the 

 chink of the glottis. 



Stuttering is due to a want of ability to form the proper sounds 

 by the laryngeal muscles; the breathing and diaphragm are both 

 normal. 



Pathology. Paralysis of the motor nerves of the larynx from 

 the pressure of tumors, causes aphonia, or loss of voice. In aneur- 

 ism of the aortic arch the left recurrent nerve may be paralyzed from 

 pressure. The laryngeal nerves may be temporarily paralyzed by 

 overexertion and hysteria. 



If one vocal cord be paralyzed, the voice is not pure in tone, but 

 falsettolike. 



Hoarseness may be caused by mucus upon the vocal cords or by 

 roughness or laxness of the cords. Disease of the pharynx or naso- 

 pharynx and uvula may, in a reflex manner, produce a change in the 

 voice. 



APHASIA. 



Aphasia means a loss of power to produce or understand spoken 

 or written speech. 



Aphasia is a disorder of the speech, due to a lesion of the third 

 left frontal convolution. There are four different kinds of word- 

 memory, each having its seat of registration in a well-defined part 

 of the cortex. The first is the (1) auditory word-center, where the 

 sound of words is registered; (2) a visual word-center, where the 

 visual images of letters and words are registered; (3) a glosso-kinaes- 

 thetic center, where the combined impressions which pass to the 

 brain as a result of the movements of the lips, tongue, palate, larynx, 

 and other parts concerned in articulate speech, are registered; (4) 

 a cheiro-kinaesthetic center, where sensory impressions resulting from 

 the movements made in writing are stored up. From the glosso- 







