1.1.2　Dermis

The dermis develops from the mesoderm，which is mainly composed of connective tissue，containing nerves，blood vessels，lymphatic vessels，muscles，and skin appendages.The dermis can be divided into the papillary layer and the reticular layer from shallow to deep，but there is no clear boundary between the two layers.The papillary layer is a papillary bulge that protrudes toward the bottom of the epidermis and is connected to the epidermal process in a crisscross shape.The reticular layer is thicker，is located below the papillary layer，and has larger blood vessels，lymphatic vessels，and nerves.

The dermis connective tissue is composed of collagen fibers，elastic fibers，matrix，and many cells.Collagen fibers and elastic fibers are interwoven with each other and buried in the matrix.The cells in the normal dermis include fibroblasts，tissue cells，and mast cells，etc.Collagen fibers，elastic fibers，and matrix are all produced by fibroblasts.(https://www.daowen.com)