126 ELEMMINTS OF HIPPOLOQY. 



It requires about eight months to grow a new hoof. This 

 growth of wall is faster at the toe than at the heel, and in the 

 unshod horse the wear is greater at the toe, consequently the 

 wall is maintained at the proper height. 



The hoof grows faster during a moist, warm season, if the 

 animal is in good health, than it does in dry or cold weather, or 

 when the horse is debilitated. The hoof often shows the effect 

 of the more favorable season by a thickened ring in the horn. 

 Such rings, when of healthy growth, are called grass rings. 



When the foot strikes the ground the tendency is to force 

 the cofSn-bone down into its wedge-shaped seat. This is pre- 

 vented by the intimate union between the sensitive and in- 

 sensitive laminae (whose folds, if spread to their complete de- 

 velopment, would cover more than a square yard), and by the 

 elastic resistance of the frog, the plantar cushion, the flexor 

 tendon, and the lateral cartilages. 



The sensitive and insensitive laminae not only dovetail into 

 each other in the direction of their length, but they are also 

 provided with mu' ! iple barbs that also interlock and resist any 

 sliding. tendency. All these elastic media unite in receiving the 

 shock of impact and transmit it gradually through the bones 

 and tendons of the legs and to the muscles above for its final 

 decomposition. 



The foot itself actually spreads out slightly, and the con- 

 cavity of the sole is reduced at the moment of impact. For this 

 reason, except when necessary to prevent the undue spreading 

 of the heels while the horse is in motion, shoes should be left 

 open at the heels. 



The plantar surface of the foot is shown in Figure 85, after 

 it has been levelled off to receive the shoe. The frog and its 

 cleft are clearly seen. The doubling back of the wall to form 

 the bars shows plainly at the heels. The line of demarcation 

 between the sole and wall is shown in the dark line paralleling 



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