Which feature differentiates a synovial joint from cartilaginous joints?

• A. Lack of a cavity.
• B. Bones connected by dense fibrous tissue with no joint cavity.
• C. Cartilage with limited movement.
• D. Fluid-filled joint cavity that allows lubrication.

Answer: (D)

The key idea is that synovial joints have a fluid-filled cavity that lubricates the joint, allowing smooth and wide-ranging movement. This joint cavity, lined by a synovial membrane and containing synovial fluid, is the hallmark that sets synovial joints apart from other types.

In cartilaginous joints, bones are joined by cartilage and there is no such joint cavity, so movement tends to be more limited. Fibrous joints also lack a joint cavity and connect bones with dense fibrous tissue.

Therefore, the feature that differentiates a synovial joint is the presence of a fluid-filled joint cavity that provides lubrication.