During fetal development, the entire body derives from three layers, called germ layers, the ectoderm, mesoderm, and endoderm.

胎发育过程由三个组成，分别是：外、与内。

This constitutes a defect or absence of the vertebral arches, due to failure of mesoderm to organize over the region of the defect, and it may or may not involve the underlying meninges and neural tissue.

这椎弓的畸形或缺失，这是由于不能在缺陷区域处生长；椎弓的缺失可能影响其下的脑脊膜和神经组织。