172 



INSPIRA TION. 



by certain muscles which move the ribs, and by the 

 diaphragm. 



The ribs during expiration slope downwards, the end 

 of each attached to the spinal column being higher than 

 the end attached to the breast-bone (Fig. 5). When we 

 draw a breath, certain muscles pull up the front ends 

 of the ribs. When this occurs, the breast-bone is pushed 

 farther away from the back-bone, and the depth of the 

 chest between breast-bone and spinal column is in- 

 creased. 



That raising the front end of the ribs must push the 

 breast-bone forwards may be readily understood by ex- 

 amining Fig. 46. In the figure, ab represents the spinal 

 column, and st the breast-bone. 

 The position of the ribs in expira- 

 tion is indicated by the rods c and 

 d '; their position in inspiration, 

 by the dotted lines c 9 and d' . It is 

 clear that when the ribs are raised 

 the sternum must be separated 

 farther from the back-bone. 



21. Action of the Diaphragm dur- 

 ing Inspiration. The diaphragm 

 (d, Fig. i) is a dome-shaped muscle, 

 with its hollow side turned to- 

 wards the abdomen. When it 

 contracts, it flattens, and thus in- 

 creases the chest-cavity. At the same time, it pushes 

 down the liver, stomach, and intestines. These make 



In inspiration ? What is the result of raising the front ends of the 

 ribs? 



21. Form of the diaphragm ? How altered when it contracts ? Re- 

 sult as regards the chest? The abdomen ? 



FIG. 46. Diagram of a 

 model to illustrate how the 

 chest-cavity is increased from 

 before back when the front 

 ends of the ribs are raised, ab 

 represents the spinal column; 

 st, the breast- bone; c, d, the 

 ribs in expiration; c', d', the 

 ribs in inspiration. 



