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FIG 4. Diagrams showing normal development of the vertebral column (adapted from Moore [4]).
A, At 4 weeks' gestation, the vertebral body develops around the notochord. Each mesenchymal segment contributes to the formation of the vertebrae above and below and to the formation of the intervertebral disk.
B, At 5 weeks' gestation, development of the vertebral centrum is complete and the notochord regresses.
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