Os Metacarpi Magnum (fig. 303), or large metacarpal, or canon bone, extends from the knee to the fetlock joint, which it assists in forming. It is rounded in front, flattened behind, and very dense and strong throughout. Its superior extremity articulates with the lower row of knee bones, and in front, below the articulation, towards the innerside, is a roughened prominence into which the tendon of its extensor muscle is inserted. At the back part of the upper end there is a roughened patch for the attachment of the suspensory and check ligaments. The lower extremity is rounded from before to behind, and divided by a prominent ridge into two nearly equal parts or condyles. The whole of this end is covered with cartilage, and articulates with a corresponding surface formed by the upper extremity of the os suffraginis, or large pastern bone, and the two small sesamoid bones behind.

Fig. 302. - Fore Leg from the Radius.

1 Radius. 2 Radio-carpal Joint. 3 Pisiform. 4 Cuneiform. 5 Lunar. 6 Unciform. 7 Os Magnum. 8 Small Metacarpal Bone. 9 Large Metacarpal Bone. 10 Sesamoid Bone. 11 Fetlock Joint. 12 Suffraginis or First Phalanx. 13 Superior Pastern Joint. 14 Os Coronae or Second Phalanx. 15 Navicular Bone. 16 Pedal Joint. 17 Os Pedis or Third Phalanx.