3 weeks: The baby’s eyes and spine are visible. The brain has two lobes. 4 weeks: The baby’s heart is beating. Brain components and internal organs are beginning to develop. 7 weeks: The cerebrum has divided into two hemispheres. When the upper lip is tickled, the arms move backwards. 9 weeks: More than 90% of the baby’s bodily structures found in a full grown human are present. The medical classification changes from an embryo to a fetus, most development involves growth instead of the formatio