The white line is the visible transition between the horn of the hoof wall and the horn of the sole. The horn of the white line is comparatively soft horn that consists of the horn produced by the terminal papillae on the end of the dermal laminae (interlaminar horn) and the horn that has grown down between the dermal laminae (laminar horn). This gives the white line a striated appearance. In a longitudinal section, the white line extends from the solar margin to the distal end of the laminar corium.

The white line must not be confused with the unpigmented innermost layer of the hoof wall (stratum medium). This layer is immediately adjacent to the white line and is often paler in colour than the white line itself; it can be differentiated by the lack of striations.