<unk>  as seen in a pregnant woman<unk>  (Latin for "black<unk> , often referred to as a pregnancy<unk>  is a<unk> r hyperpigmentation that commonly appears on the abdomen. The brownish streak is usually about a centimeter (0.4 in) in width. The<unk> runs vertically along the midline of the abdomen from the pubis to the umbilicus, but can also run from the pubis to the top of the abdomen. For pregnant women,<unk>  is attributed to increased melanocyte-stimulating hormone made by the placenta, which also causes melasma and darkened nipples. Fair-skinned women show this phenomenon less often than women with darker pigmentation.<unk>  typically disappears within a few months after delivery. Although<unk>  is rarely discussed outside pregnancy, males and females of all ages may have it. Except in pregnancy, both sexes have highest and equal prevalence of<unk>  from age 11 to 15. This increase in prevalence could be the result of hormonal changes during puberty. After age 15, the prevalence of<unk>  in males declines. In females it is often just a sign of unusually high benign estrogens. The prevalence for both sexes drops to below 10% after age 30. Additionally, it can appear after a short-interval weight gain. Or could be a sign of hormonal imbalance, genetic disease, cancer, inflammation and even fungal infection.
Linea nigra
Alpinia nigra
Tapetum lucidum
Tinea nigra
Habenular nuclei
Glia limitans
Corona radiata 
Collateral eminence