Which architectural feature is characterized as the "anatomy" of an arch?

The voussoir is indeed characterized as the "anatomy" of an arch. It refers specifically to the wedge-shaped stones or bricks that make up the arch itself. Each voussoir is placed in a way that contributes to the overall structural integrity of the arch, as they are angled to fit together and distribute weight evenly. The keystone, which is the central voussoir at the apex of the arch, plays a crucial role in locking the other voussoirs into place and maintaining the curve of the arch.

In contrast, columns serve structural purposes and can support an arch or a roof, but they are not part of the arch's anatomy. An entablature is the horizontal structure supported by columns and does not relate to the arch's specific components, while a pediment is a triangular space typically found above a portico, often serving decorative purposes and providing visual balance, rather than being a structural element of the arch itself. Thus, the voussoir is the defining feature that describes the construction and function of an arch's structure.