Calcar

Calcar, from Latin calcar meaning spur, is a term used in biology to describe a spur-like projection on a body part or organ. In human anatomy, the calcar femorale is a vertical plate of dense trabecular bone along the posteromedial aspect of the femoral neck, contributing to structural support of the femoral head and serving as a radiographic landmark. In bats, the calcar is a cartilaginous spur on the inner hind limb that supports the uropatagial membrane, helping to stabilize the wing during flight. In botany, calcar denotes a spur, a tubular projection at the base of a petal or sepal that often contains nectar and functions in pollination; many flowers with nectar spurs rely on specialized pollinators to access the nectar. The term’s broad use reflects a common morphological idea: a projection or extension that adds structure or a specialized function to the organism’s anatomy or floral organ. While the details differ across disciplines, the underlying concept remains consistent: calcar refers to a spur-like feature that plays a role in support, movement, or reproduction.