Ulna and Humerus

The ulna is one of two bones found in the forearm.  It forms a hinge joint with the humerus and a pivot joint with the radius, giving the lower arm the range of motion to bend and rotate the hands.   On anatomical drawings, the ulna and radius may be hard to distinguish,  so consider that the ulna is the bone that is on the pinky side of the hand  (think: P-U, the pinky is stinky, to remember that the pinky and the ulna go together.)     The ulna can also be identified by the shape of it’s head which is wrench-like where it articulates with the humerus.

When learning structures of the bone, it is helpful to look at all of the bones.  The olecranon process of the ulna (3) fits in to the olcranon fossa of the humerus, forming a hinge joint.    The coronoid process fits into the coronoid fossa of the humerus.

ulna

1 = coronoid process 2=Trochlear Notch 3= Olecranon Process 4=Styloid Process 5 = Radial Notch

The trochlea of the humerus, which is a cylindrical structure fits into the trochlear notch of the ulna, making a point for the elbow to rotate.

humerus-labeled

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