12. Radius, or Bone of the Fore-arm.—The radius is a long bone, and occupies a vertical position between the humerus and the carpus.
13. Ulna, or Bone of the Fore-arm.—The ulna is an irregular bone, in form triangular, with the base uppermost, and is placed on the supero-posterior or (upper and back) part of the radius.
14. Carpus, or Knee.—The carpus, knee or wrist, as it is incorrectly termed in quadrupeds, is composed of seven and often of eight small, irregular bones arranged in two rows of three each, one above the other, the seventh being at the back of the three in the upper row, and the eight, when present, in a similar position with respect to the lower row. Their names are as follows: scaphoid, lunar bone, cuneiform bone, trapezium, trapezoid, os magnus, unciform, pisiform, which is not always present.
15. Os Metacarpi Magnus, Metacarpal or Cannon Bone.—The large metacarpal, or cannon bone, is a long, straight bone, placed in a vertical direction. Its superior or upper extremity articulates with the carpus and its inferior or lower extremity articulates with the os suffraginis and the two sesamoids.
16. Ossa Metacarpi Parva, or Splint Bones.—The two small metacarpal, or splint bones, tuberous in form (marked or covered with projections) at the carpus and tapering distally (lower portion), are attached to the large bone, one on each side of its posterior (back) surface, by ligaments in the young animal, and by ossification (union of bone) in most grown up, and in all old animals.
17. Proximal Phalanx, Os Suffraginis, or Large Pastern Bone.—The os suffraginis, or large pastern bone, passes obliquely downwards and forwards, and articulates with the cannon bone above, and the median phalanx or os coronae below. It belongs to the class of long bones.
18. Great Sesamoid Bones.—These bones, two in number, are placed side by side at the postero-inferior (back and lower) part of the metacarpus and postero-superior (back and upper) part of the os suffraginis; they are irregular in shape, their back parts are covered with cartilage, for the passage of the flexor tendons of the digit or the last four bones of the limb. Their superior or upper surface is roughened, and their sides, which are grooved for the reception of the suspensory ligament. (This is called the fetlock joint.)
19. Median Phalanx, Os Coronae, or Small Pastern Bone.—The second phalanx, os coronae, or small pastern bone, has no marrow canal, and belongs to the class of irregular bones. It is inclined, like the os suffraginis, obliquely downwards and forwards, and is partly covered by the hoof. The upper portion of this bone articulates with the os suffraginis and the two sesamoids, the lower part articulates with the os pedis.
20. Distal Phalanx, Os Pedis, or Coffin Bone.—The third, or ungual phalanx, os pedis, or coffin bone, is an irregular bone situated within the hoof, and, when in a healthy state, corresponding somewhat to it in shape, being semilunar in form, with the convexity to the front. This bone is very hard and porous, having many openings for the transmission of arteries and veins. In this bone we notice the wall, the sole, the tendonous surface, the articular surface, and the alae or wings. This bone articulates with os coronae superiorly (upper) and posteriorly it articulates with the os navicular bone.
21. Os Naviculare.—The naviculare, third or small sesamoid, or shuttle bone, is an irregular bone, situated with its long axis transversely, behind and below the os coronae, and behind the os pedis, with both of which it articulates, the articulation of the three forming the so-called coffin joint. The lower surface of this bone is important as it is covered with cartilage, and together form a kind of a pully over which plays the great flexor perforans muscle. The remaining portion of the anterior limb or front leg, will be considered under anatomy of the foot. The navicular bone can be plainly seen on Plate [VII], anatomy of the foot.