Which of the following is NOT a class of joints?

The correct answer is "D" because medullary does not refer to a class of joints. Instead, "medullary" relates to the medullary cavity, which is the central cavity of bone where marrow is stored. In contrast, synovial, fibrous, and cartilaginous joints are well-established classifications of joints based on their structural and functional characteristics.

Synovial joints are characterized by a fluid-filled joint cavity that allows for various types of movement, making them the most movable type of joint in the human body. Fibrous joints are connected by dense connective tissue and generally allow for little to no movement, as seen in the sutures of the skull. Cartilaginous joints are connected by cartilage and offer more movement than fibrous joints but less than synovial joints; an example is the joints between the vertebrae.

Understanding these categories is fundamental in anatomy and kinesiology, particularly for group fitness specialists who may need to apply knowledge of joint types to exercise selection and injury prevention strategies.