I think we have enough torso studies now.
It's time for some legs.
The thigh is build very similar to the arm.
On the front side is a triceps (tri = three), consisting of a bundle of three muscles, to straighten the leg.
The triceps on the back of your arm does exactly the same.
Of course the counterpart is the biceps (bi = two).
Logically it is placed on the opposite side of the leg / arm to pull on the bones so the joint forms an angle.
It's really simple.
About the illustration:
1: back view of the thigh
2: outer side view
3: front view
4: inner side view
The part that takes practise (as always) is to understand the forms in a threedimensional way.