Does prayer necessitate prostration on seven or eight limbs?

The Prophet, peace and blessings be upon him, commanded prostrating on seven bones: the forehead—and he pointed with his hand to his nose—the two hands, the two knees, and the ends of the two feet. The forehead is the primary part for prostration, and the nose is a تابع (subordinate) to it. The meaning of them being one organ in nomenclature and expression, but not in ruling, is that prostrating on the nose alone without the forehead is not sufficient.