84 



HUMAN PHYSIOLOGY 



THE LUNGS. The lungs, two in number (Fig. 23), 

 are contained in the cavity of the thorax or chest. 

 This cavity is bounded by the spine and ribs behind, 

 and by the breast bone and cartilages or gristly ends 

 of the ribs in front. It is a highly elastic part of the 

 skeleton, the elasticity being due largely to the pres- 

 ence of the rib cartilages just noted. The need for 



Fig. 23. THE LUNGS IN POSITION VIEWED 

 FROM THE FRONT. 



They rest on the diaphragm or midriff. 

 The heart is shown in outline. 



elasticity can be appreciated when regard is had to 

 the constant movements the chest exhibits in the act 

 of breathing. The lungs are suspended freely in the 

 chest and communicate with the cavity of the mouth 

 and with the air by means of the trachea or windpipe 

 (Fig. 24) at the upper part of which we find situated 

 the larynx or organ of voice (1). The windpipe is 

 kept open and patent by the pressure of gristly rings 

 which can easily be felt in the front of the throat. 



