The main difference between the joint capsule and the joint cavity is that the joint capsule contains the joint cavity, and the joint cavity is an internal component of the joint capsule. The joint capsule is composed of two layers, the outer layer is made up of fibrous membrane and the inner layer is made up of synovial epithelial cells. These two layers make up the entire joint capsule that envelops the entire joint, including the articular cartilage within the joint, some of the bone, and the ligaments within the joint. The joint cavity is a relatively small cavity made up of the joint capsule and articular cartilage, and is certainly smaller in extent than the joint capsule. It is mainly filled with synovial fluid and ligaments, and some joint cavities do not contain ligaments.