The carpometacarpus is the fusion of digits (carpals and metacarpals) – essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally flattened and with a large hole in the middle. In flightless birds, however, its shape may be slightly different, or it might be absent entirely. It forms the tip of the wing skeleton in birds. To it, most of the primary remiges attach. The alula, by contrast, is formed by the thumb, which doesn't complete… (More on Carpometacarpus)