The central nervous system appears in the middle of the 3rd week of the development as a thickened area of the embryonic ectoderm, the neural plate. Its lateral edges become elevated to form the neural folds, which approach each other and fuse in the middle, thus forming the neural tube.
At the cranial and caudal end of the embryo the neural tube is temporarily open and communicates with the amniotic cavity by the way of the cranial and caudal neuropores. The neural tube differentiates into the central nervous system, consisting of the brain and spinal cord, and the neural crest, which gives rise to the most of the peripheral nervous system.
The neural canal becomes the ventricular system of the brain and the central canal of the spinal cord.

1. Notochord
2. Intermediate zone of neural crest
3. Neural groove
4. Neural crest
5. Neural fold
6. Dorsal root ganglion
7. Neural tube
8. Surface ectoderm

1. Neural plate
2. Primitive node
3. Primitive streak
4. Cut edge of amnion

1. Primitive streak
2. Cut edge of amnion
3. Neural fold
4. Neural groove
5. Somite
6. Primitive node

1. Pericardial bulge
2. Anterior neuropore
3. Somite
4. Posterior neuropore