Answer:
a. Hinge
Explanation:
The hinge joint is one of the types of synovial joints. It is also known as the ginglymus joint. In a hinge joint, the convex surface of one bone fits into the concave surface of another bone. The hinge movement produced by these joints is analogous to the opening and closing of a hinged door. Hinge joints are uniaxial or monaxial in nature since movement around a single axis, such as flexion and extension, is allowed by these joints.
For instance, the interphalangeal joints between the rounded heads of phalanges and the concave bases of the distal phalanges are the hinge joints between the phalanges of the fingers and toes.
