Vertebratesby Alvin Silverstein, Dr Alvin/Virginia/Robert Silve
In this book we'll focus on our closet relatives in the animal kingdom: the vertebrates. In a vertebrate embryo, the nerve cord and notochord are separate at first. But then the notochord develops into the spine, which surrounds and protects the nerve cord (spinal cord). The spine is not a stiff, solid tube. It is made of a series of parts, the vertebra, linked together like beads in a necklace. The holes in the center of each vertebra form a channel through which the spinal cord passes.
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