A firm, resilient connective tissue of vertebrates and some invertebrates. Isolated pieces act as a skeleton to provide support and anchor muscles, or cartilage is with bone to contribute its resilience and interstitial growth to bony skeletal functions. Cartilage comprises a firm extracellular matrix synthesized by large, ovoid cells (chondrocytes) located in holes called lacunae. The matrix elements are water bound by the high negative charge of extended proteoglycan (protein-polysaccharide) molecules, and a network of fine collagen fibrils. The elements furnish mechanical stability, give, and tensile strength, but allow the diffusion of nutrients and waste to keep the cells alive. Generally, blood vessels reach only to the perichondrium of fibrous connective tissue, wrapping around the cartilage and attaching it to other tissues.