196 HANDBOOK OF PHYSIOLOGY. 



tion of the pillars of the fauces and descent of the soft palate, chiefly 

 through the nose, and any offending matter is thence expelled. 



Speaking. In speaking, there is a voluntary expulsion of air 

 through the glottis by means of the expiratory muscles. 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 sound 

 is produced. The sound is moulded into articulate speech by the tongue, 

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

 nothing to do with articulation. 



Singing. Singing resembles speaking in the manner of its produc- 

 tion ; the laryngeal muscles, by variously altering the position and de- 

 gree of tension of the vocal cords, producing the different notes. Words 

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

 tongue, teeth, lips, etc. 



Sniffing. Sniffing is produced by a rapidly repeated but incomplete 

 action of the diaphragm and other inspiratory muscles. The mouth is 

 closed, and the whole stream of air is made to enter the air-passages 

 through the nostrils. The alae nasi are, commonly, at the same time, 

 instinctively dilated. 



Sobbing. Sobbing consists of a series of convulsive inspirations, at 

 the moment of which the glottis is usually more or less closed. 



Laughing. Laughing is made up of a series of short and rapid ex- 

 pirations. 



Yawning. Yawning is an act of inspiration, but is unlike most of 

 the preceding actions, as it is always more or less involuntary. It is 

 attended by a stretching of various muscles about the palate and lower 

 jaw, which is probably analogous to the stretching of the muscles of the 

 limbs in which a weary man finds relief, as a voluntary act, when they 

 have been some time out of action. The involuntary and reflex char- 

 acter of yawning probably depends on the fact that the muscles con- 

 cerned are themselves at all times more or less used involuntarily, and 

 require, therefore, something beyond the exercise of the will to set them 

 in action. For the same reason, yawning, like sneezing, cannot be well 

 performed voluntarily. 



Sucking. Sucking is not properly a respiratory act, but it may be 

 most conveniently considered in this place. It is caused chiefly by the 

 depressor muscles of the os hyoides. These, by drawing downwards and 

 backwards the tongue and floor of the mouth, produce a partial vacuum 

 in the latter : and the weight of the atmosphere then acting on all sides 

 tends to produce equilibrium on the inside and outside of the mouth as 

 best it may. The communication between the mouth and pharynx 

 is completely shut off by the contraction of the pillars of the soft palate 

 and descent of the latter so as to touch the back of the tongue ; and the 

 equilibrium, therefore, can be restored only by the entrance of some- 



