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A major characteristic of 16 week fetuses is the substantial growth of subepicardial vessels and nerve fibers. A, the atrioventricular junction (AV) is especially rich in nerves (N) and veins (Ven). B, development of arteries (Art) and veins has progressed to the apical region of the ventricles. Slides were stained with Masson trichrome. Magnification bar = 100 μm.
