224 RESPIRATION. 



In all these expulsive actions the diaphragm is quite 

 passive; and when it is fixed, it is in consequence of 

 the closure of the glottis (which by preventing the exit of 

 air from the lungs prevents its upward movement), not 

 from any exertion on its own part. 



In females, during parturition, almost an exactly similar 

 action occurs, so far as the diaphragm and abdominal 

 walls are concerned, to that which takes place in a strain- 

 ing effort at expulsion of urine or faeces. The contraction 

 of the uterus, however, is both relatively and absolutely 

 more powerful than that of the bladder or rectum, although 

 it is greatly assisted by the inspiratory effort, by the fixing 

 of the diaphragm, and by the action of the abdominal 

 muscles, as in the other acts just described. In parturi- 

 tion, as in vomiting, the action of the abdominal muscles 

 is, to a great extent, involuntary more so than it com- 

 monly is in the expulsion of faeces or urine ; but in these 

 latter instances also, in cases of great pain and difficulty, 

 it may cease to be a voluntary act, and be quite beyond 

 the control of the will. 



In speaking, there is a voluntary expulsion of air through 

 the glottis by means of the abdominal muscles ; and the 

 vocal cords are put, by the muscles of the larynx, in a 

 proper position and state of tension for vibrating as the 

 air passes over them, and thus producing sound. The 

 sound is moulded into words by the tongue, teeth, lips, 

 etc. the vocal cords producing the sound only, and having 

 nothing to do with articulation. 



Singing resembles speaking in the manner of its pro- 

 duction ; the laryngeal muscles, by variously altering the 

 position and degree of tension of the vocal cords, pro- 

 ducing the different notes. "Words used in the act of 

 singing are of course framed, as in speaking, by the 

 tongue, teeth, lips, etc. 



Sniffing is produced by a somewhat quick action of the 

 diaphragm and other inspiratory muscles. The mouth is 



