In fact the wall is the hardest horn, the sole is softer than the wall, and the heel is softer than the sole. The white line is the softest horn and forms the junction between the sole and the wall. In the claw the epidermis is the horny hoof. The dermis or corium contains the nerve and blood supply and is inside the epidermis of the claw. The corium produces the horny claw and if the corium is damaged it cannot produce healthy horn, thus lameness occurs.
Healthy corium equals healthy horn and diseased corium equals diseased horn.
The most common causes of lameness in cattle are from damage to the corium. So heel horn is formed by the perioplic corium. Therefore, the pedal bone is firmly attached and suspended inside the toe of the normal hoof. The laminar corium also produces most of the white line. The solear corium produces the solear horn.