ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY. ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY.
Endoscopic image of the human embryo in vivo after 4 weeks, showing the retina of the eye (dark spot)- after another week the lens and cornea will form in front of it. To the right is the developing brain. The blood vessels (running diagonally, left to right) connect the embryo to its yolk sac, which continues to supply it with nourishment until the sixth week of development. The endoscope, a series of lenses and a fibre-optic light source, is inserted through the cervix and manipulated until a "window" into the amniotic sac is found (an area where the amniotic wall is thinner).
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