Medically reviewed by Susan Bard, MDMelanonychia, also known as a dark or black line on the nail, causes a streak of dark ...

Nail ridges are grooves or raised lines that form on the nail plate and ... or external nail damage. Vertical nail ridges: These run from the base of the nail to the tip and are generally more ...

For one thing, our bodies are quite symmetrical. When you draw a vertical line down the center of a body, the left and right sides are almost mirror images of each other. Human bodies also show ...