Muscles start to develop. The embryo’s arm and leg buds become visible, and the “neocortical cells appear. The neocortex is the seat of complex thinking and reasoning.” This feature is present in no other mammal. The embryo is has grown to 6 to 7 millimeters long (about ¼ inch). The baby’s blood flows in their veins, separate from their mother’s blood.
-Week 5: The Pituitary gland, or master gland, is forming. “The baby’s mouth, ears, and nose are taking shape.”
-Week 7: The first fully developed nerve cells appear on the top of the baby’s “spinal cord, beginning the construction of the brain stem,” regulating vital functions such as breathing, the heartbeat, and blood pressure.
-Week 8: All organs are present, complete, and functioning (except the lungs). The heartbeat is sturdy, and the stomach produces digestive juices. The liver is producing blood cells, and the kidneys are functioning.