All ectodermal organs, e.g. hair, teeth, and many exocrine glands, originate from two adjacent tissue layers: the epithelium and the mesenchyme.

• 所有外胚层器官，例如毛发，牙齿以及一些外分泌腺，均来源于相互邻结接的两层组织：上皮层和间充质层。