In hooves there are three void spaces that tell us as much about the feet and their state of health as the physical structures do.
The central sulcus is the space between the two legs of the frog. An optimal central sulcus is situated at the caudal half of the frog and opens out of the end of the foot in the shape of a triangular wedge.
The collateral grooves are the spaces between each side of the frog and the bar lateral to it. In an optimal foot both the sides of the frog and the bar will be straight, and the caudal end of the collateral groove will be occluded by the frog curtain.