A layer of dense irregular connective tissue that surrounds the cartilage of developing bone, consisting of two separate layers: an outer fibrous layer and inner chondrogenic layer. The fibrous layer contains fibroblasts, which produce collagenous fibers. The chondrogenic layer remains undifferentiated and can form chondroblasts or chondrocytes. Perichondrium is a type of connective tissue, and also functions in the growth and repair of cartilage. Once vascularized, the perichondrium becomes the periosteum.