HORSESHOEING. 19 



3. The bones of the tarsus, or hock (25), which are six small, 

 irregular bones disposed in three rows, one above another. The 

 OS calcis, or heel-bone, and the astragalus are in the uppermost 

 row, and are the most important. The former projects above 

 the true hock-joint from behind, to form a long lever, the upper 

 end of which is called the " point of the hock," and the latter 

 articulates with the tibia. The tarsal (hock) bones articulate 

 below with — 



4. The metatarsal bones (26 and 27), which are longer, and the 

 cannon narrower from side to side, than the corresponding meta- 

 carpal bones, but are otherwise similar. 



5. The phalanges of a- hind limb (28 to 31) are also narrower 

 than those of a fore-limb, but are nearly alike in other respects. 



All the horse's bones present small, but more or less distinct 

 openings (nutrient foramina) for the passage of blood-vessels and 

 nerves. Many bones possess roughened elevations and depres- 

 sions, to which ligaments, tendons, or muscles are attached. 

 With the exception of the os pedis, all bones are enveloped in a 

 sort of " bone-skin" called periosteum. The bones unite among 

 themselves to form either movable or immovable unions. A mova- 

 ble union between two or more bones is termed a "joint," or 

 articulation. The articulating ends of the bones, presenting 

 on one side a convex surface (head or condyle) and on the other 

 a corresponding concave surface (glenoid or cotyloid cavity), are 

 covered with elastic articular cartilage. The bones are bound 

 together by means of ligaments, which are tough, fibrous, cord- 

 like, or sheet-like structures. Ligaments are either (1) capsular 

 or {2) funicular (cord-like). Every articulation in the limbs pos- 

 sesses a capsular ligament, and all, except the shoulder-joint, 

 have several funicular (cord-like) ligaments. The capsular liga- 

 ments are lined upon their inner face with a delicate membrane 

 (synovial membrane) which secretes the synovia, or "joint 

 water," whose function is to lubricate the joint and prevent fric- 

 tion ; they enclose the joint in a sort of air-tight cuff or sack. 

 The funicular ligaments are very strong and often large, and are 



