Final answer:
A pivot joint is a uniaxial diarthrosis type of joint that allows for rotation only, such as the atlantoaxial joint in the cervical spine and the proximal radioulnar joint in the forearm.
Step-by-step explanation:
The type of joint where a rounded portion of one bone fits into a ring formed by another bone and ligaments is known as a pivot joint. This joint allows for rotation around a single axis, making it a uniaxial diarthrosis joint. Rotation only occurs in this type of joint.
An example of a pivot joint is the atlantoaxial joint, which occurs between the C1 (atlas) and C2 (axis) vertebrae in the cervical spine, enabling the head to turn from side to side. Another is the proximal radioulnar joint in the forearm that allows for the rotational movement of the wrist.A pivot joint is a uniaxial diarthrosis type of joint that allows for rotation only, such as the atlantoaxial joint in the cervical spine and the proximal radioulnar joint in the forearm.