Scanning electron micrograph (SEM) of the structure of a feather from a lanner falcon (Falco biarmicus). The central shaft, or rachis, of the feather is seen initially, with the underside of the numerous parallel barbs seen branching from it. The barbs further divide into barbules, which interlink thanks to small terminal hooks called barbicels. The rachis has been freeze-fractured in preparation here, revealing its internal structure in cross-section. This honeycomb-like structure is strong while still being light. The lanner is a large falcon found in Africa, southeastern Europe and western Asia.