Reece R L, Butler R
Aust Vet J. 1984 Dec;61(12):403-5. doi: 10.1111/j.1751-0813.1984.tb07174.x.
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.
对16只幼平胸鸟类（10只美洲鸵鸟、3只鸸鹋和3只鸵鸟）从1日龄到12周龄的长骨进行了观察。孵化时，所有长骨都含有与生长板相连的大软骨锥和骨皮质。在1周龄时，这些胚胎锥的周边开始骨化，并且在一些骨骼中，锥与生长板分离。在3周龄时，近端和远端胫跗骨中仍存在软骨胚胎锥，狭窄的软骨桥将锥与生长板相连。在3周龄美洲鸵鸟的其他长骨以及6、8和12周龄平胸鸟类的长骨中不存在胚胎锥。其他早成鸟，如火鸡幼雏和鸡，孵化时其长骨中有胚胎软骨锥，这些锥在胫跗骨中持续存在到1至2周龄。3周龄平胸鸟类胫跗骨中存在大的胚胎软骨锥可能是一种正常现象。认识到这一特征对于正确鉴别平胸鸟类常见的肌肉骨骼疾病至关重要。
