SCOTT CAMAZINE / SCIENCE PHOTO LIBRARY SCOTT CAMAZINE / SCIENCE PHOTO LIBRARY
Twelve week old foetus. The alizarin staining technique has been used in order to show the bone development of the foetus. At this stage the crown-rump length (sitting height) of the foetus is about 8cm and its weight is around 18g. The head of the foetus constitutes about one half of the crown-rump length and decreases to one third by the beginning of the fifth month and to one fourth at birth. The face has all the human characteristics but the ears are still primitive. Movements begin at this time but are usually not felt by the mother. At twelve weeks most of the internal organs have formed and the sex may be determined by external (ultrasound) examination.
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