Final answer:
The synovial joint that does not have at least one rounded or convex surface is the a) plane joint. Plane joints have flat or slightly curved surfaces allowing for limited sliding movements and are considered multiaxial joints with constraints.
Step-by-step explanation:
The student's question pertains to types of synovial joints and their movements. Synovial joints are characterized by the presence of a fluid-filled joint cavity that allows for a range of motion between the bones that articulate at the joint. For the question about which synovial joint does not have at least one rounded or convex surface, the answer is the plane joint.
Plane joints, also known as gliding joints, consist of flat or slightly curved surfaces that slide against one another. Unlike other synovial joints, plane joints don't have a rounded or convex articulating surface. They are classified as multiaxial joints because they can technically allow for movements along multiple axes, yet these movements are often limited by the surrounding ligaments or bone structures. Examples include the intercarpal joints of the wrist and the intertarsal joints of the foot. The answer is option a.