TISSUEPIX / SCIENCE PHOTO LIBRARY TISSUEPIX / SCIENCE PHOTO LIBRARY
Foetus. Skeleton of a 16 week old human foetus. Hardened bone appears yellow here. Gaps between the ends of bones, such as the fingers, are filled with cartilage (not seen), which forms the matrix upon which hard bone forms. The bones of the skull are seen growing from thin filaments (upper centre). At this stage of development the foetus weighs 200 grams and has a crown-rump length of up to 14 centimetres. Stained with Alizarin red dye.
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