Pivot joint Pivot joint In animal anatomy, a pivot joint (trochoid joint, rotary joint, lateral ginglymus) is a type of synovial joint. In pivot joints, the axis of a convex articular surface is parallel with the longitudinal axis of the bone. According to one classification system, a pivot joint like the other synovial joint —the hinge joint has one degree of freedom. Note that the degrees of freedom of a joint is not the same as the same as joint's range of motion. Pivot joints allow for rotation, which can be external (for example when rotating an arm outward), or internal (as
Bell's hinge-back tortoise Bell's hinge-back tortoise Bell's hinge-back tortoise ("Kinixys belliana") is a species of African tortoise, from the family Testudinidae. It has the hinge that characterizes all tortoises in the genus "Kinixys". There are several subspecies (some of which may actually be separate species; see below) and the Bell's hinge-back tortoise is subject to wide variation throughout its extensive range. Both the specific name, "belliana", and the common name are in honor of English zoologist Thomas Bell. Bell's hinge-back tortoise is a medium-sized light brown tortoise. They can grow up to 22 cm. On the back of its shell, the tortoise has