What is the central rib that runs the length of the vane in a feather called?

The term that describes the central rib running the length of the vane in a feather is the rachis. This structure is crucial as it provides support and stability to the feather, allowing the barbs, which extend from either side of the rachis, to create the surface area needed for flight. The barbs are the smaller, branch-like structures that interlock to form the feather's interlocking design, which is essential for insulation and aerodynamic functions.

Other terms in the question refer to different parts of the feather: the quill is the hollow, lower part of the feather that anchors it to the bird’s skin; the barb refers to the smaller filaments that branch off from the rachis; and the culmen is a term that describes the upper ridge of a bird’s beak, unrelated to feather structure. Understanding the distinctions among these terms enhances comprehension of feather anatomy and function in birds.