TISSUEPIX / SCIENCE PHOTO LIBRARY TISSUEPIX / SCIENCE PHOTO LIBRARY
Foetus. Bones in the skull of a 16 week old foetus. Hardened bone appears dark red. The bones of the skull are seen growing from thin filaments, which radiate from a central point (primary ossification centre). The frontal bone (centre left) and parietal bone (centre right) are seen here. The bones meet at sutures, and are joined by connective tissues. At this stage of its development the foetus weighs around 200 grams and has a crown-rump length of up to 14 centimetres. Alizarin red dye.
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