MUSCLE AS THE SOURCE OF MOTION. 



93 



fibre surrounds a cavUy, the cavity is lessened when the 

 muscle contracts. This is the whole source of motor 

 power in the crayfish machine. Tlie results produced 

 by the exertion of that power dej^end upon the manner 



Fig. 20. — Astnciis J{ u I'lafU'is.— The chela of the forcepp, with one side 

 cat away to show, in A, the muscles, in B, the tendons ( x 2). 

 cp, carpopodite ; jyrj), propodite ; dj}, dactylopodite ; m, adductor 

 muscle ; m', abductor muscle ; t, tendon of adductor muscle ; if, 

 tendon of abductor muscle ; x, hinge. 



in w^hich the parts to which the muscles are attached 

 are connected with one another. 



One example of this has alread}^ been given in the 

 curious mechanism of the gastric mill. Another may be 

 found in the chela which terminates the forceps. If the 



