Plausibly digitigrade

The legs and feet are the pivotal features of appearing as a faun. Horns, ears, beard, and syrinx are courtesy detail. Here are the different proportions of leg-bone lengths in goats and humans. 

Obviously, the centre of gravity of the creature must be above where he stands on the ground, otherwise he'll fall over. In practice, that puts a faun's hips exactly vertically above his hooves.

Fauns have goat legs, and so I looked in some detail at goat anatomy in order to understand what's going on under the fur.

The fundamental difficulty is that humans are plantigrade creatures, walking on the soles of their feet. Goats are digitigrade; they walk on their toes and what corresponds to a human foot becomes a long thin bone with almost no flesh, right up to the ankle, or hock.

The backward-pointing knee joint, the hock, is anatomically equivalent to the ankle in humans. The true knee is higher and, mercifully for costume design, buried in fur.

Of anatomical interest is that in animals that habitually walk, the thigh bone is proportionally longer than that of a runner. Animals that run have short thigh bones and longer lower legs.

It is fundamentally impossible to recreate an anatomically accurate digitigrade leg on a normal human without surgery or CGI.

Here are a few shots of ideas for padding that accommodate the requirements of both the human and the caprine leg.

Obviously, the costume leg will be a lot fatter than a 'real' one. What we have is something that's anatomically plausible rather than anatomically accurate.

I have started with the profile of a human skeleton. I positioned the leg slightly bent and the foot standing on tiptoe, because that's the position the leg is going to end up in when wearing the costume.

I also tweaked the coccyx into a sensibly-angled tail. It has to flow from the spine without horrible kinks. 

Next, I took the bones from the hind leg of a normal goat skeleton. I found a better lower leg in a book on caprine osteology, so I used that.

I sketched up how a caprine hind leg would look over the goat leg-bones. In order to be sure that a human leg would fit inside the same silhouette, the leg is fatter that it otherwise would be.

A human leg just about fits inside the same padding as the goat leg. This is what I have to create with foam rubber and faux fur. I need to make what efforts I can to minimise the padding to make the leg as slender as possible.