There are three main bones of the human arm: the humerus of the upper arm and the radius and ulna of the forearm. The humerus articulates with the shoulder at the gleno-humeral joint. The humerus articulates with the ulna and radius at the elbow in a complex joint, allowing for flexion of the elbow as well as pronation and supination of the forearm. The radius articulates with the carpal bones and the ulna at the wrist.
Humerus
The humerus is the long bone of the upper arm. At the shoulder, it has a rounded joint face where it joints the glenoid fossa. There are two tuberosities (bumps) at the shoulder, where several muscles attach, separated by the bicipital groove. There is a long ridge down the outside of the humerus with a bump in the center where the deltoid attaches. At the elbow, the humerus flattens out where it joins the ulna to make a hinge joint with epicondyles (bumps) on either side and depressions front and back.
Ulna
The ulna is one of the two long bones of the forearm. The ulna is largest at the elbow where it forms a hinge joint with the humerus and a pivot joint with the radius. It has a hollow face at the elbow where it joins the humerus with a large bump called the olecranon process (the sharp part of the elbow) and a smaller one called the coronoid process on either side. The ulna tapers toward the wrist where it is much smaller and has a ridge running its length ending in a small projection called the styloid process.
Radius
The other bone of the forearm, the radius, is smaller at the elbow and larger at the wrist. It has a round surface with a thin neck at the elbow where it forms a pivot joint with the ulna and a sliding joint with the humerus. There is a bump where a group of muscles attach from the elbow and upper arm called the radial tuberosity near the neck. There is a ridge, like that of the ulna, that runs the length of the bone. The radius gradually expands to a large trapezoidal shape at the wrist where it articulates with the scaphoid and lunate bones of the wrist in a condyloid type joint.
References
- "Gray's Anatomy: The Anatomical Basis of Clinical Practice;" Susan Standring (Editor); 2008
- "Trail Guide to the Body: How to Locate Muscles, Bones and More:" Andrew Biel; 2005
- "Basic Pathology;" Vinay Kumar, Ramzi Contran and Stanley Robins.Sixth Ed.;1997
