ball and socket

A form of diarthrodial articulation in which the articular surfaces are nearly flat, so that they form only an imperfect ball and socket.

It consists of a compass whose needle plays over a circle graduated to 360�, and of a horizontal brass bar at the ends of which are standards with narrow slits for sighting, supported on a tripod by a ball and socket joint. n

They have rhombic, ganoid scales, a heterocercal tail, paired fins without an axis, fulcra on the fins, and a bony skeleton, with the vertebrae convex in front and concave behind, forming a ball and socket joint