123 



§ 121. The larynx is a box with unyielding sides, 

 TDiit the loindpipe is a flexible tube, formed, at its 

 front, by a series of three-quarter hoops. The 

 space between the ends of these hoops, that is the 

 back of the windpipe, is filled out by a yielding 

 membrane. The windpipe thus somewhat resem- 

 bles the body of a snake, if we suppose the ribs to 

 join below, forming one piece mth the scutae (§ 44) 

 and the vertebrse to be removed above. 



§ 122. It is plain, we think, not only that con- 

 siderable motions of torsion and counter-torsion 

 must take place in the windpipe, but also, that its 

 connections with the lower jaw, to be given in the 

 next section, show that those twistings must exert 

 a powerful reflex influence on the motions of the 

 whole body. We might also appeal to horsemen, 

 who well know how different the effects of the 

 bit are from those of the cavesson, a difference 

 which can be explained only by the fact that move- 

 ments of the lower jaw affect the lungs, and 

 changes in the lungs affect the trunk. It is when 

 the spur, acting on the false ribs near the dia- 

 phragm, alters the filling of the lungs, in counter- 

 action to any attempt of the lower jaw to stiffen 

 itself into one piece with the head, that that perfect 



