A new brain
The embryo forms the basic structures that become the brain and spinal cord between the third and fourth weeks of its life. A groove running along the length of the embryo folds up to make a cylinder called the neural tube. Three different compartments start to grow at the head end of the tube, which will become the forebrain, midbrain and hindbrain. The embryonic brain then balloons - it gets 30 times bigger and fills with fluid.