This is the longest bone in the fore limb, and extends from the humerus above to the knee below. Its superior extremity is divided into two concavities by a small ridge, and corresponds with the two convexities and the dividing furrow observed on the lower extremity of the humerus, with which it articulates to form the elbow-joint. Behind, towards the outer side, it presents a long roughened surface, where it forms a bony union with the ulna.

The lower extremity is somewhat irregular, and articulates with the four bones comprising the upper row of the knee. In front there are three grooves over which three tendons play in passing down the limb to their points of insertion. Each tendon is supplied with a synovial membrane to facilitate its movements over the bone during flexion and extension of the knee.