II HABITS AND NATURAL HISTORY OF THE FROG 27 



to be raised up and thrown forward. '^ If," says Hartog, 

 " we inject with melted cocoa butter colored with car- 

 mine or alkanet, and keep up the pressure until the mass 

 sets, we find that it fills an enormous lymph sac between the 

 muscle and the body of the hyoid, extending through the 

 median intermuscular fissure into the tongue itself, sending 

 branches between the fan-shaped ramification of the intrin- 

 sic muscles at the edges of the tongue and into its terminal 

 dilatations." According to Hartog, the contraction of the 

 mylohyoid muscle expels the lymph from the subhyoid space 

 into the tongue and thus effects the protrusion of this organ. 



Locomotion. — The locomotion of the frog is effected by 

 leaping and swimming, and in both of these operations the 

 long hind legs play the chief part. In the ordinary resting 

 position the body is inclined upward in front, being sup- 

 ported on the fore legs, which are held in a peculiar twist so 

 that the large thumb points nearly backward ; the posterior 

 part of the body rests upon the ground, and the hind limbs 

 are folded up ready for a spring. No preliminary move- 

 ments are required in order to get the animal in readiness 

 for escape. By a sudden extension of the hind legs the 

 body is propelled through the air. In leaping, the fore 

 limbs are used more to hold up the anterior part of the 

 body and to point the animal in the desired direction of 

 movement than as actual organs for propulsion. If one 

 causes a frog to leap in various directions, it will be observed 

 that the body is adjusted before each leap in a new direc- 

 tion by the movements of the fore limbs. An ordinary 

 specimen of Rana pipiens may leap from two to three feet. 



The movements of the hind legs in swimming are very 

 much like those performed in jumping. In both operations 

 the hind legs are alternately drawn up in the form of a Z and 

 quickly extended. As they are pushed back, the toes are 



