Shoulder:A structure made up of two main bones: thescapula(shoulder blade) and thehumerus(the longboneof the upperarm). The end of the scapula, called the glenoid, is a socket into which the head of the humerus fits, forming a flexibleball-and-socket joint. The scapula is an unusually shaped bone. It extends up and around theshoulder jointat the rear to create a roof called theacromionand around theshoulderjointat the front to constitute the coracoidprocess. The shoulder joint is cushioned bycartilagethat covers the face of the glenoid socket and the head of the humerus. The joint is stabilized by a ring of fibrous cartilage around the glenoid socket that is called thelabrum. Ligaments connect the bones of the shoulder and tendons join these bones to surrounding muscles. Thebicepstendonattaches the bicepsmuscleto the shoulder and helps stabilize the joint. Four short muscles that originate on the scapula pass around the shoulder where their tendons fuse together to form the rotator cuff.
