The temporomandibular joint is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium (skull), and the lower jaw bone called the mandible. The unique feature of the TMJs is the articular disc. The disc is composed of fibrocartilagenous tissue (like the firm and flexible elastic cartilage of the ear) which is positioned between the two bones that form the joint. The disc divides each joint into two. The lower joint compartment formed by the mandible and the articular disc is involved in rotational movement - this is the initial movement of the jaw when the mouth opens.
