HORSESHOEING. 21 



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

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

 The OS calcis, or heel-hone, and tlie astragalus are in the upper- 

 most 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 hones (26 and 27), which are longer, 

 and the cannon narrower from 'side to side, than the correspond- 

 ing metacarpal bones, but are otherwise similar. 



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

 rower 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 de- 

 pressions, 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 

 movable 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 mth 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 

 possesses 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 cuflF or sack. 

 The funicular ligaments are very strong and often large, and 



