The embryo is 17 mm long from crown to rump and weighs 2.7 grams. The neck is taking shape, and the head is gradually facing upwards. The embryo is beginning to grow muscle fibres. A dividing wall between the right and left sides of the heart and four heart chambers have been formed. Both milk teeth and permanent teeth are forming. The nervous system continues to develop. In both genders, the inner sexual organs are forming. Female embryos have now immature eggs in their ovaries. There are approximately 10 million immature eggs at this point. At the time of birth the number will have dropped to 1 million, and at the time of puberty there will be 400,000 eggs left. The embryo is responsive to touch.