Pointed Arch
Masonry arches and vaults are composed of wedge-shaped stones called voussoirs that must be supported on a temporary framework, called centering, until the arch or vault is completed, at which time the stone press tightly against one another and become self-supporting.
Such construction requires firm lateral bracing, as an arch or vault exerts not only a downward thrust but also lateral thrust, which is an outward, over-turning force that must be counter-acted if the arch or vault is to remain in equilibrium. While all arches behave in a similar manner structurally, their profiles vary considerably.
Pendentive
The Pendentive is a constructive device permitting the placing of a circular dome over a square room or an elliptical dome over a rectangular room. The pendentives, which are triangular segments of a sphere, taper to points at the bottom and spread at the top to establish the continuous circular or elliptical base needed for the Dome.
In masonry the pendentives thus receive the weight of the dome, concentrating it at the four corners where it can be received by the piers beneath.