The arms begin to form at about 3 weeks and the fingers from 6 weeks on. The baby can close his fingers and thumb and he will open his mouth in response to pressure applied at the base of the thumb. At first when his hands touch his mouth the baby turns his head away, though his mouth opens. Later he may turn his head towards his hands and put his finger into his mouth to suck it. Finger nails are present at 7 months.