Cartilage is a tough flexible connective tissue with variable characteristics depending on its structure and use in the body. Structural cartilage forms the larynx and supports the soft tissue of the nose for example, whilst fibrous cartilage forms the intervertebral discs. Bone is formed on a cartilage matrix in the embryo and persists as cartilaginous epiphyseal growth plates in bones from which they grow, the plates being replaced by bone as the horse matures. A specialized form, articular cartilage, caps the end of the long bones in joints, providing a rubbery shock absorber lubricated by synovial fluid. These protective articular cartilage caps are supported by microscopic boney columns. When the bone columns are defective the overlying cartilage may collapse leaving a cavity in the covering cap as part of the disease called Osteochondrosis Dissecans or OCD. Cartilage in joints is also subject to trauma as well as wear and tear and may become thin or degenerate as part of osteoarthritis.