324 SKELETON OF THE HORSE. 



The unciform, magnum, and trapezoid articulate with the 

 metacarpal bones. Normally these are five in number, as seen 

 in man ; but in the horse only one entire digit remains, ihc third ; 

 portions of the second and fourth are found as the so-called 

 "splint-hones'' (fig. 187, S). The metacarpal bone of the horse 

 is the cannon-hone (Co), and the two rudimentary ones the 

 splint-bones, one on each side of the cannon-bone, uniting with 

 it about halfway down. The remaining bones of the fore-limb 

 constitute the horse's foot. The foot is composed of three 

 bones : the one uniting with the cannon-bone is called the 

 pastern (Pas), which is the largest ; this is followed by the 

 coronet-hone (Cm') ; the last, or coffin-bone (Co/), being hidden 

 in the hoof. These form the true digit, the equivalent of our 

 third finger. There are also present two detached bones, or 

 sesamoid bones. One of these sesamoid bones is present at the 

 back of the joint formed by the cannon and pastern (Ses) ; the 

 other, the navicular hone, is found behind the junction of the 

 coronet and coffin bones inside the hoof, ^^arious bony deposits 

 occur abnormally in this region, such as "side-bone" and "ring- 

 bone.'' ".Side-bone" is a calcareous deposit on the sides of the 

 coffin-bone. " Eing-bone " is a similar deposit on the coronet. 



The postc-1-ior arch and limi are homologous to the anterior. 

 The posterior arch (fig. 188) is called the pelvic arch or hip- 

 girdle, and is made up of two large bony masses united in their 

 middle line, the ossa innominata. Each os innominatum is 

 formed by three bones known as the ilium (1), ischium (12), and 

 pubes (9), the six forming a kind of bony ring, the pelvis, which 

 is much larger in the female than the male. The ilium is a 

 triangular bone projecting forwards, and forms the so-called 

 haunch-bone. There are two noticeable parts ia it, the anterior 

 spine and the posterior spine, the latter pointing upwards, the 

 former forwards. The ischium passes backwards towards the 

 tail. The pubes are the two flat bones which unite beneath 

 at a point of union called the pubic symphysis. The pubes 

 are perforated by the two large obturator foramina (10). The 



