MECHANISM OF RESPIRATORY ACTIONS. 181 



to the position of the soft palate. The stomach communicates 

 with the exterior of the body through the ossophagus, pharynx, 

 and mouth; while below 7 , the rectum opens at the anus, and 

 the bladder through the urethra. All these openings, through 

 which the hollow viscera communicate with the exterior of the 

 body, are guarded by muscles, called sphincters, which can 



FJO. 65. 



act independently of each other. The position of the latter is 

 indicated in the diagram. 



Let us take first the simple act of sighing. In this case 

 there is a rather prolonged inspiratory effort by the diaphragm 

 and other muscles concerned in inspiration ; the air almost 

 noiselessly passing in through the glottis, and by the elastic 

 recoil of the lungs and chest-walls, and probably also of the 

 abdominal walls, being rather suddenly expelled again. 



16 



