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

胚胎发育过程胚组成，分别是：外胚、胚与内胚。

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.

这导致了椎弓的畸形或缺失，这是胚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。