Webster: wedge shaped piece at crown of arch that locks the other pieces

inplace, something on which associated things depend for support.

Lexicon: a center stone in an arch, bearing lateral and vertical stress. Note:

sacrum identified as center stone; biped weight bearing legs document

sides.

Keystone sacrum engineered design by physics. Identified by triangular

wedge shaped, locking horizon base with bi - lateral vertical sacro-iliac

semi - lunar articular biped junctions.