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                                                Embryo (labels) - histology illustration
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                                                Transverse section of a human embryo of the third week to show the differentiation of the primitive segment. (Kollmann.) ao. Aorta. m.p. Muscle-plate. n.c. Neural canal. sc. Sclerotome. s.p. cutis-plate. 
 
Histology illustration courtesy of Gray's Anatomy.
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