fenestra

Fenestra is a term derived from Latin meaning window. In anatomy, it refers to a natural opening or window-like gap in a bone or organ, often large enough to accommodate nerves, vessels, or muscles. The plural is fenestrae. The concept is used across vertebrate anatomy and paleontology to describe openings in the skull and other structures that affect function and appearance.

In skull anatomy, fenestrae are notable in the study of amniote evolution. Many groups exhibit temporal fenestrae, including anapsids (no openings), synapsids (one opening behind the orbit), and diapsids (two openings, an upper and a lower). The pattern of fenestrae has evolved through various lineages and is a key feature in reconstructing relationships among reptiles, birds, and mammals. In mammals, the ancestral temporal openings have been altered through evolution, resulting in different skull configurations and muscle arrangements.

In the middle ear, two fenestrae connect the middle ear with the inner ear: the fenestra vestibuli (oval window) and the fenestra cochleae (round window). These openings transmit sound-induced vibrations and help regulate fluid movement within the inner ear.

Outside anatomy, the term fenestra appears in other contexts. In botany, fenestrations describe leaf perforations that resemble windows, seen in several plant species as a form of adaptive leaf morphology. The term is also used more broadly to denote any window-like opening in a structure.

Etymology: from Latin fenestra, window.