194 HANDBOOK OF PHYSIOLOGY. 



companying diagram (Fig. 160) shows that the cavity of the chest is 

 separated from that of the abdomen by the diaphragm, which, when 

 acting, will lessen its curve, and thus descending, will push downwards 

 and forwards the abdominal viscera ; while the abdominal muscles have 

 the opposite effect, and in acting will push the viscera upwards and 

 backwards, and with them the diaphragm, supposing its ascent to be 

 not from any cause interfered with. From the same diagram it will be 

 seen that the lungs communicate with the exterior of the body through 



FIG. 160. 



the glottis, and further on through the mouth and nostrils through 

 either of them separately, or through both at the same time, according 

 to the position as the soft palate. The stomach communicates with the 

 exterior of the body through the oesophagus, pharynx, and mouth ; while 

 below the rectum opens at the anus, and the bladder through the ure- 

 thra. All these openings, through which the hollow viscera communi- 

 cate with the exterior of the body, are guarded by muscles, called sphinc- 

 ters, which can act independently of each other. The position of the 

 latter is indicated in the diagram. 



