This is the leg structure for my species Icealos.
The most notable feature is the spur on the back after the second joint.
That spur was used for hanging on to things while stationary. Like a tree.
Most upper Digitigrades do not have that extra bone in the upper area. That present in the Icealos because it helps support, and strengthen, and act as a spring when they jump from high distances.
In between (Not present) the bones that make up the upper two halves of the leg is a dense webbing of a elastic organic material similar to cartilage. it acts as a spring. When impacted, the bones bow out slightly, that material in between snaps it back, thus enabling the Icealos to run, and jump, faster and higher.
I used this as Ref. The middle one: http://www.arlis.org/docs/vol1/5238.....62/posture.jpg
Edit: I used pencil and paper, but put it into black and white with my scanner. Thats why its dark.