Scapula

"Scapula" is the technical name for the shoulder blade. It is a flat, triangular bone that lies over the back of the upper ribs. The rear surface can be felt under the skin. It serves as an attachment for some of the muscles and tendons of the arm, neck, chest and back and aids in the movements of the arm and shoulder. It is well padded with muscle so that great force is required to fracture it. The back surface of each scapula is divided into unequal portions by a "spine." This spine leads to a "head," which bears two processes - the "acromion process" that forms the tip of the shoulder and a "coracoid process" that curves forward and down below the clavicle (collarbone). The acromion process joins a clavicle and provides attachments for muscles of the arm and chest muscles. The acromion is a bony prominence at the top of the shoulder blade. On the head of the scapula, between the processes mentioned above, is a depression called the "glenoid cavity." It joins with the head of the upper arm bone (humerus).

Clavicle

The clavicle is the collarbone. There are two of these bones, each curved al little like an "f," that join the top of the breastbone (sternum) to the shoulder blade (scapula). The clavicles support the arms and transmit force from the arms into the central skeleton.

Bursae of The Shoulder

A "bursa" is a fluid-filled sac, lined with synovial membranes, that occurs near a joint. There are several bursae associated with the shoulder joint. The major ones include the "subscapular bursa," located between the joint capsule and the tendon of the subscapularis muscle; the "subdeltoid bursa," between the joint capsule and the deep surface of the deltoid muscle; the "subacromial bursa," between the joint capsule and the under surface of the acromion process of the scapula (shoulder blade); and the "subcoracoid bursa," between the joint capsule and the coracoid process of the scapula. Of these, the subscapular bursa usually is continuous with the synovial cavity of the joint cavity, and although the others do not communicate with the joint cavity, they may be connected to each other. All joints contain bursa, however, the shoulder has eight different bursa (the most of any joint in the body).

Condyles of The Humerus

At the lower end of the humerus (upper arm bone) and the femur, there are two smooth condyles (rounded processes of the bone): a knob-like "capitulum" on the lateral side and a pulley-shaped "trochlea" in the middle. The capitulum unites with the radius (smaller lower arm bone) at the elbow, and the trochlea is a notch which joins ligaments to the head of the ulna (larger lower arm bone). Above the condyles on either side are "epicondyles," which provide attachments for muscles and ligaments of the elbow. The one toward the center of the arm is the "medial epicondyle," and the one to the side is the "lateral epicondyle."

Humerus

The humerus is the bone of the upper arm. The smooth, dome-shaped head of the bone lies at an angle to the shaft and fits into a shallow socket of the scapula (shoulder blade) to form the shoulder joint. Below the head, the bone narrows to form a cylindrical shaft. It flattens and widens at the lower end and, at its base, it joins with the bones of the lower arm (the ulna and radius) to make up the elbow. Some people say the "funny bone" is named because it is next to the humerus. It really isn't a bone at all, but is the ulnar nerve, which passes under a prominence of the humerus, where it is vulnerable. To find the funny bone, put the point of the right elbow on a table. Above and to the left of the point is a big knob. When it is struck, the blow pushes the nerve against this knob, causing temporary paralysis. It is no laughing matter, but it is a "funny" feeling.