108 



part of the movement. Compressed by one gath- 

 ering they aid in initiating the next ; supporting 

 the chest they form, at their working centre, 

 (common with that of the ophidian S) the true 

 centre of force (§ 99) ; and they fulfill another 

 and more important function in the completion of 

 each movement of locomotion , which will be spoken 

 of in connection with the lower jaw. 



§ 106. Within the ribbed portion of the trunk 

 in the higher animals, are the lungs, and below this 

 portion the stomach, bowels, &c. The two are sepa- 

 rated by a sheet of tendon stretched horizontally 

 across the bottom of the chest and attached by 

 muscular fibres to the upper edges of the lowest 

 ribs, and to the cartilage-prolongations which go 

 from them to the lower end of the breast bone. 



This sheet of tendon with its muscular border is 

 called the Diaphragm. In our description of it 

 and of the muscular fibres which stretch it we shall 

 speak in general terms, aiming simply at convey- 

 ing such an idea of its action as may be of service 

 in explaining the process of " Setting-up," when 

 we come to that final object of our work. 



The diaphragm is described in anatomical works 

 as consisting of three lobes, whose shape and situ- 



