The first stage of development is called the "embryonic" and lasts until about the end of the second month. Early in the development of the |embryo|, the central nervous system appears as a groove in the ectoderm along the midline of its back. This is the rudimentary nervous system; the large end develops into the |brain| and the rest forms the |spinal cord|. By the end of the 6th week the |spinal cord| has started its development. The earliest appearance of the skeletal system is during the second month of interuterine life.
