By the end of this week, your baby measures about one-third of an inch from crown to rump. (Doctors use this "sitting height" to track early growth because baby's legs are hard to measure). Curled up, she's about as big as a pea. But she's a pea with personality: her facial features are starting to emerge -- small hollows that will become eyes, inner ears, and the beginnings of mouth and tongue.
Around the embryo's tiny body, a first layer of skin forms, delicate and translucent. The ends of the arm buds flatten into little paddles called "hand plates." By the end of next week, fingers will have formed. In this early stage, they are webbed, like duck's feet.
Amazing changes are taking place in the embryo's brain right now. Its cells are dividing into three sections. First is the forebrain, home base to the human personality. This is where problems will be solved and the avalanche of information gathered by the senses -- sounds, smells, tastes -- will be processed. Next comes the midbrain, which will serve as a relay station, coordinating messages and sending them on to their final destinations in the body. Last is the hindbrain, responsible for regulating the heart, breathing, and muscle movements. All three parts, working together, form the miraculous command center that is the human brain.