Tinamous have a very long, keeled, breastbone with an unusual three-pronged shape. This bone, the sternum, has a central blade (the Carina sterni), with two long, slender lateral trabeculae, which curve to either side and nearly touch the keel posteriorly. These trabeculae may also be thought of as the rims of two large that incise the posterior edge of the sternum, and extend almost its whole length. Tinamous have a proper semicircular furcula, with no trace of a hypocleidium. There is an acute angle between the scapula and coracoid, as in all flying birds. The pelvis has an open ilio–ischiatic fenestra that incises the posterior edge between the ilium and ischium, as in all paleognathes. Tinamous have no true pygostyle, their caudal vertebrae remain unfused, as in ratites.