How is the skeleton formed in an egg?: Laboratory

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	How is the skeleton formed in an egg?

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Research

Bones of the vertebrate tend to be fossilized, which enables the scientist to trace the evolutional process. We observe the developmental process of the chicken from the egg, and study the mechanism of bone formation, especially the formation of the backbones and the ribs. In the embryos in the egg (Fig.1), there are tissues called somites which are the origin of the ribs and the backbones. The shape of the bones can be changed by manipulating there rudiments under microscope. The mechanism of bone formation can be elucidated by studying which type of operation changes the shape of the bones.

If the somites are inverted rostro-caudally (Fig.2), the ribs are formed as shown in Fig. 3. Compare this with the normal shape in Fig. 4. The direction of the spine is opposite. By performing such experimental operations, it becomes possible to know that there is a rostro-caudal axis in a somite, and this axis determines the shape of the bones. This fact could not be obtained by observation alone.