The remains of the roughed-out state in which the panel was originally carved can be seen around the heads of the horse and Bellerophon. The roughed-out form of the horse's head was clearly quite a lot larger than the final form and allowed for a range of details to be added during more detailed carving. All of this rough work was hidden from the ground by the angle at which the horse's head projects.
The front of the horse's head is shaped with the flat chisel.
Even though this is one of the lowest quality carvings on the Sebasteion and a considerable amount of rough work is left around both the horse and Bellerophon, the carver still went to a lot of effort to carve the horse's leg in the round.