Instead of a longer article, I went for one article per structure.
Here are the others:

• Hoof Wall
• Sole
• Frog & Collateral Grooves
• White Line
• Bars
• Coronary Band & Periople

HEELS / HEEL BUTTRESS

The heels are strong pillars supporting the back of the foot, made of wall.

They should have a decent volume compared to the rest of the foot, be strong and parallel to the wall at the toe (dorsal wall). Ideally, they should be almost identical on the same foot (height, thickness, horn quality, orientation, size, location in the foot – not too far forward) but also on both feet (front or back).

They play a major role in impact management, together with the frog, as well as weight bearing in general.

  • Healthy
  • Under-run
SOLAR VIEW
Left: Relatively healthy heels, with a large, upright, flat and balanced ground-contact area. The blue lines are parallel and the green lines are almost the same length. (The picture is slightly angled anti-clockwise.)
Right: Here we see much less symetry between the lines. The green lines are much longer than on the previous examples: run forward / under-run heels. The heels are very long and also folded over the sole, not upright.
  • Healthy
  • Under-run
LATERAL VIEW
Notice the difference of distance between the heel bulb and the actual heel on both feet.
Here are almost absent heels. This was taken just after unshoeing. They built up with time and stimulation.
Left: before trim, under-run and folded over heels of unequal length. Right: after trim, far from perfect, but more balanced.

HEEL BULBS

Located above the heels, they should form nice, supple and round “balls” at the back of the foot. They should sit softly above the heels and have relaxed skin between them.

They house the lateral cartilages and the digital cushion. The way the heel bulbs look and feel give you an indication on how healthy the cushion and cartilages are.

  • Healthy
  • Distorted
Notice the symetry difference between the lines.
  • Developped
  • Atrophied
On the left is a developped back of the foot (heel bulbs) but atrophied on the right.
  • “Sheared heels”
  • Relaxed heel bulbs
On the left is what is called sheared heels. Notice how narrow the heels are compared to the right picture. Hence the tiny narrow frogs very often observed on those feet.