Final answer:
The ball-and-socket shoulder joint is formed by the head of the humerus and the glenoid cavity of the scapula, allowing extensive movement but having compromised stability.
Step-by-step explanation:
The shoulder joint, known as the glenohumeral joint, is a ball-and-socket joint. The articulating surface in the shape of a 'ball' is the head of the humerus while the 'socket' part is formed by the glenoid cavity of the scapula. This joint allows the largest range of motion of any joint in the body. The functionalities such as flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation of the humerus are provided by this unique joint design. Despite the extensive mobility, the shoulder joint's stability is somewhat compromised due to the shallow depth of the glenoid cavity. Support is alternatively provided by structures like the glenoid labrum, which deepens the socket, and intrinsic ligaments such as the coracohumeral ligament and glenohumeral ligaments. Additionally, the muscles that cross the joint, forming the rotator cuff, play a critical role in maintaining the joint's stability.