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Mammary glands. Historical illustrations of the appearance and internal structure of the mammary glands. A normal breast (upper left) is compared to the breast when pregnant (upper right) and after giving birth (centre). These last two show larger nipples and are swollen to produce milk to feed a newborn baby. A surface detail of a nipple is at centre left. The lactiferous ducts bringing milk to the nipple are seen at centre right and at lower left (blue), within the breast. The mammary gland (white) that produces the milk is shown in section at lower right. Colour lithograph by Fairland from The Viscera of the Human Body, 1840. Based on drawings by Bagg. (KEYSTONE/SCIENCE PHOTO LIBRARY/SHEILA TERRY)