CHAP. XXXI.] SPEECH. 445 



or whether the disturbance is not excited in the centre through the 

 influence of an afferent nerve. Anything irritating the delicate 

 mucous membrane of the larynx creates violent spasmodic action 

 of the muscles of the glottis, in which those of respiration fre- 

 quently take part, through the medium of the afferent superior 

 laryngeal nerve. 



Pressure upon the inferior laryngeal excites spasmodic cough, 

 which often forms an important symptom of aneurism, or of 

 mediastinal tumor. Section or disease of the inferior laryngeal 

 nerve completely destroys the power of vocalization. 



Stammering, at least in the greater number of instances, is an 

 affection of the nervous system, not of the articulating organs. It 

 consists in a defective control over the will, and an imperfect 

 power of co-ordinating the muscles of speech. Stammering is 

 much increased by any mental excitement, sudden surprise, etc., 

 and one of the most important points to be kept in view in the 

 treatment of this condition, is to avoid all cause of excitement to 

 the patient, and to prevent him from thinking about his condition 

 as much as possible, so that he may gradually obtain that com- 

 mand over the movements of the muscles, which is required for 

 conversation. 



Speech. In the vocal apparatus, notes of very various pitch can 

 be produced at will. The different sounds of the voice have been 

 shown to be due to variations in the size of the aperture of the 

 glottis and in the tension of the chordae vocales. The vocal organ, 

 however, is not capable of producing those articulate sounds by 

 which we are enabled to communicate to each other our ideas ; 

 but this end is obtained by an alteration taking place in the cavity 

 situated above the glottis, and in the position of the organs which 

 it contains. 



The most important conditions affecting speech are, first, the 

 size of the oral aperture, secondly, the size of the buccal cavity, 

 and, thirdly, the position of the tongue. 



The production of vowel sounds, which are continuous and can 

 be prolonged at will, depends entirely upon the size of the buccal 

 cavity and outlet. In the sound of the a in aA, these are opened 

 to their widest extent, while in sounding a in fate the buccal 

 cavity requires to be much reduced in size, by the lateral expan- 

 sion and elevation of the tongue. When we sound the e in me, 

 cavity and outlet are made still less. The o in no results from a 

 still further diminution of the oral aperture while the buccal 

 cavity is much increased ; and in the oo in boot the former is 



