1. Appearance of cranial flexure and torsion. Flexion means the bending of the body about a transverse axis as one might bend the head forward at the neck. In the head region, the neural tube bends in the region of the mesencephalon so that the forebrain and hindbrain are nearly parallel. This is the cranial flexure. The second flexure called cervical flexure occurs in the posterior region of the brain, at the level of the rhombencephalon. These two flexures give the anterior region of the embryo a C-like structure and a transverse section of the embryo at the anterior end exhibits two neural tubes, two notochords, and two foreguts.
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