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The onset of osteogenesis in the developing chick limb.

The pattern of the onset of osteogenesis in each of the skeletal elements of the developing limbs of the chick embryo is described using Alizarin-red-stained whole mounts. Grafting experiments where 6-day unossified cartilage rudiments are placed into 4-day host wings show the initiation of ossification to be a programmed event. Truncation experiments show this to be the case not only for the initial onset of osteogenesis, but also for each region of each element. These results are discussed in terms of morphogenetic events occurring in the early wing bud.