The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.

• 中胚层中间胚芽层，位于外胚层和内胚层之间，最终发育成结缔组织、肌肉、骨骼、泌尿系统及循环系统