Embryonic Development

Day 56: By approximately 2 months after conception the developing embryo is recognizably human. Only 1" in length, most of the organs have been formed by this time.

Day 41: In the earlier stages of the embryo’s development the human features are not as apparent. Although the heart has a steady rhythm, the embryo is less than ½" long.

Day 27: Less than a month after conception the first sign of an upper limb is present. The developing embryo is covered with skin. But a small opening may be seen near the bottom of the developing spine.

Day 23: At day 23, the embryo is curved and the back portion is less curved and the back portion is rolled into a tube called the neural tube. The lower end becomes the spine and the upper end, the brain.

Day 22: Just one day before, the neural tube begins to close in a zipper like fashion from the middle toward the end.  Closure will normally be complete within a week.

Neural tube defects occur when the neural tube fails to close completely. Failure of the neural tube to close over the lower spine causes spina bifida. 

Failure to close in the region of the developing brain causes anencephaly or encephalocele.  Encephalocele shown below.