The equine bulb is formed from keratin in the same manner as the sole and again this keratin is softer and more liable that the keratin found in the hoof wall. The frog ensures that the wall of the hoof is forced outwards when weight is put on the limb thus ensuring that the 'hoof mechanism' (see equine section below) functions correctly. The ruminant/pig 'bulb' provides the hoof with the caudal and mid-hoof contact area with the ground and is chiefly involved in weight bearing. The bulb inserts into the V-shaped sole. The bulb is made of relatively soft material, mainly inter-tubular horn and is of a considerable thickness.