NEW VERSION HERE

From left to right - Human Leg, Canine/Feline Leg, Equine Leg

Yellow - Toenail
Orange - Toe
Blue - Ball
Pink - Heel
Purple - Calf
Green - Knee
Red - Thigh

Not 100% accurate in terms of precise placement/proportion however this is a general guide intended to point out...
IT IS NOT A BACKWARDS SECOND KNEE
It is a heel. Most animals walk on the ball of their foot, equines walk on their toes (the hoof is their toenail, grown out over the toe).