THEORY OF THE EAKTH. 85 



Thus not only the class, but the order, the genus, 

 and even the species, are found expressed in the 

 form of each part. 



In fact, in order that the jaw may be able to 

 seize, it must have a certain form of condyle ; 

 that the resistance, the moving power, and the 

 fulcrum, should have a certain relative position in 

 regard to each other ; and that the temporal 

 muscles should be of a certain size ; the hollow 

 or depression, too, in which these muscles are 

 lodged, must have a certain depth ; and the zy- 

 gomatic arch, under which they pass, must not 

 only have a certain degree of convexity, but it 

 must be sufficiently strong to support the action 

 of the masseter. 



In order that the animal may be able to carry 

 off its prey, it must have a certain degree of vi- 

 gour in the muscles which elevate thehead; whence 

 there results a determinate form in the vertebrae 

 from which these muscles take their rise, and in 

 the occiput into which they are inserted. 



In order that the teeth may be able to cut flesh, 

 they must be sharp-edged, and must be so in a 

 greater or less degree, according as they have flesh 

 more or less exclusively to cut. Their base will 

 be solid, according to the quantity and size of the 

 bones which they have to break. The whole of 

 these circumstances must necessarily influence 

 the development and form of all the parts which 

 contribute to move the jaws. 



