1.1.4.4　Nail

The nail is the largest skin appendage of the human body，covering the extended side of the end of the fingers（or toes），consisting of multiple layers of tight keratinocytes.The main functions of the nail include protecting the tip of the finger，improving the sense of discrimination，assisting the finger to complete fine movements，scratching，and aesthetic functions.The exposed part of the nail is called nail plate，shaped like a convex rectangle.The crescent-shaped light-colored area at the proximal end of the nail is called nail lunula.The skin around the nail plate is called nail wall，and the portion of the nail plate deep into the proximal skin is called nail root.The skin beneath the nail plate is called nail bed，and those below the nail root are called nail matrix，which is the germinal structure of the nail.The subdermal dermis is rich in blood vessels.The fingernail growth rate is about 1 cm every 3 months，and the toenail growth rate is about 1 cm every 9 months.The trait and growth rate are affected by factors such as disease，nutritional status，environment，and lifestyle.(https://www.daowen.com)