Some observations on the development of the long bones of ratite birds

Summary Observations were made on the long bones of 16 young ratite birds (10 rheas, 3 emus and 3 ostriches), from 1‐day‐old to 12 weeks of age. At hatching all long bones contained large cartilaginous cones which were continuous with the growth plates, and an osseous cortex. At one week of age ossification had commenced on the periphery of these embryonic cones and in some bones the cones had become separated from the growth plates. At 3 weeks of age the embryonic cones of cartilage were still present in the proximal and distal tibio‐tarsi and narrow cartilaginous bridges connected the cones to the growth plates. Embryonic cones were not present in other long bones of this 3‐week‐old rhea nor in the long bones of ratites 6, 8 and 12 weeks of age. Other praecocial birds such as turkey poults and chickens have cones of embryonic cartilage in their long bones at hatching and these persist in the tibio‐tarsi till one to 2 weeks of age. The presence of large cones of embryonic cartilage in the tibio‐tarsal bones of 3‐week‐old ratite birds is probably a normal phenomenon. Awareness of this feature is necessary for the correct differential diagnosis of the prevalent musculoskeletal disorders of ratite birds.