126 



like,"^ articulations of the lower jaw is easily recog- 

 nized on opening or shutting it. The weight of 

 the lungs and the contractions of the digastric 

 muscles would continually open it by drawing on 

 its front part, were it not for several powerful mus- 

 cles on both sides which easily keep it closed, so 

 long as the windpipe loops do not come too far for- 

 ward. 



On the plan of describing only such parts as 

 seem necessary to the explanation of oiu* subject, 

 we may here select the two " Temporal muscles,'" 

 one on each side of the head, as representing the 

 forces which close the lower jaw, and which thus, 

 as will be presently explained, complete the series 

 of motions that give a double twist to all the 

 springs of the body. 



For the lower attachments of the temporal mus- 

 cles a projection of bone rises from the upper edge 

 of the lower jaw on either side, in front of the 

 hinge-like articulation with the skull, and, from 

 these projections, the muscles spreading out Hke a 

 fan, fix themselves for their upper attachment over 

 the surface of the temples (whence their name). 



§ 125. When the lower jaw is closed, each di- 



* In the lion, &c., they are complete hinges ; in man and the horse 

 there is also a lateral movement. 



6* 



