THE REGION OF THE FOREARM is formed by two bones, the _radius_ and _ulna_. The radius is the principal bone and is classed among the long bones. The ulna is an elongated flat bone. It is attached to the external portion of the posterior face of the radius and extends above the superior extremity of this bone to form the point of the elbow. The radius articulates with the upper row of knee bones. The muscles of this region, the antibrachial, are divided into two sub-regions, anterior and posterior. They originate superiorly from the lower extremity of the arm bone and the superior extremities of the bones of the forearm, and terminate toward the lower extremity of the region in tendons that become attached to the bones of the knee, cannon and digit. THE KNEE OR CARPAL region is formed by seven short bones that are arranged in two rows. They form a series of articulations. These are the articulations between the two rows, between the bones of each row, and between the upper and lower rows and the neighboring regions. Nearly all the motion takes place in the articulation between the upper row and the principal bone of the forearm. THE CANNON OR METACARPAL region is formed by three bones. These are the principal metacarpal or cannon bone, and the rudimentary metacarpal or splint bones. The latter are attached to the margins of the posterior face of the cannon bone. The superior extremities of these bones articulate with the lower row of carpal bones. The convex extremity of the cannon bone meets shallow depressions in the superior extremity of the first digital bone. This is termed the fetlock joint. The anterior and posterior faces of this region are travelled by the long tendons belonging to the extensor and flexor muscles of the digit. THE DIGIT OR TOE is formed by six bones, three of which are termed accessory or sesamoids. The digital bones may be given numerical names. THE APPROXIMAL OR THIRD DIGITAL BONE is the shortest long bone in the body. The two shallow articular cavities belonging to the superior extremity are completed posteriorly by the two sesamoid bones. The inferior extremity is smaller than the superior and resembles the inferior extremity of the cannon bone in shape, excepting that it shows a middle groove. The anterior and posterior faces are travelled by the tendons of the digital muscles. THE MIDDLE OR SECOND DIGITAL BONE is quite short. It articulates superiorly with the first, and inferiorly with the third bone of the digit. The superior face shows two shallow cavities, and the inferior two convex surfaces separated by a median groove. The latter face articulates with the third and navicular bones. The popular name for this articulation is the coffin joint.