THE FROG 47 
The “ventral” and “dorsal” surfaces of the hind leg are stich 
in consequence of the extreme obliquity of the pelvic girdle; 
they are really preaxial and postaxial, and correspond respectively 
to the inner and outer surfaces of the human leg. 
The muscles should be studied in a frog that has been hard- 
ened in formalin. Aid in the identification of the muscles may 
be obtained by consulting figure 70 of Holmes’ Biology of the 
Frog, or figure 11 of Marshall’s The Frog. The origin and 
insertion of each muscle should be carefully determined, and 
then located on the skeleton of the frog. The action of the 
muscle may sometimes be tested by pulling it gently, but this is 
often impracticable in preserved material; the action of a muscle 
may generally be inferred from its position. For the more 
accurate determination of the action of a muscle, stimulation by 
an electric current in the freshly-killed frog is required. 
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 codperation with 
other muscles. Having completed your table compare it with the 
description in Holmes’ Biology of the Frog, correct your own if 
wrong, and then verify the corrections on your specimen. 
In removing the skin from the hind limb of the frog, be careful 
not to remove with it the thin muscle which is attached 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 by dividing it 
transversely in the middle and reflecting the two halves, leaving 
the origin and the insertion intact. 
1. 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 exténds somewhat 
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 
