68 THE FROG 



position. For the more accurate determination of the action 

 of a muscle, stimulation by an electric current in a freshly- 

 killed frog is required. 



In removing the skin from the hind limb of the frog, be 

 careful not to remove with it the thin muscle which is at- 

 tached to the skin along the posterior side of the thigh. The 

 dissection of the muscles will consist mainly of separating 

 them by means of a seeker. In case it becomes necessary to 

 cut a muscle in order to expose the muscles underneath, this 

 should be done with scissors by dividing it transversely in the 

 middle and reflecting the two halves, leaving the origin and 

 the insertion intact. 



Construct a table giving the origin, insertion and action 

 of each of the muscles named below. In the description of 

 the action of a muscle, it should be stated what movement 

 the muscle would accomplish if it worked alone; the effect 

 of the contraction of a muscle is sometimes different when 

 it acts in cooperation with other muscles. Having completed 

 your table compare it with the description in Holmes' Biol- 

 ogy of the Frog, correct your own if wrong, and then verify 

 the corrections on your specimen. 



i. The thigh, (a) Superficial muscles of the preaxial 

 side. This surface is ventral when the thigh is adducted and 

 the leg extended. 



The sartorius, a narrow thin muscle which extends some- 

 what obliquely from the abductor surface of the thigh at its 

 proximal end to the adductor surface at its distal end. 



The adductor magnus, a large muscle on the adductor 

 side of the sartorius; distally it passes beneath the sartorius. 

 About its middle it receives a small slip which originates on 

 the tendon of one of the heads of the semitendinosus; this 

 will be examined later. 



