In a series of really interesting papers, Emily Giffin linked neural canal size with form and function in diverse tetrapods. This graph (from Giffin 1995b) shows how birds flying and flightless differ as goes the position of the largest parts of their spinal cords. The ostrich ( Struthio ) lacks a large spinal cord section in the anterior (brachial) part of its spinal column. Image: Giffin (1995b).