2i8 THE HORSB. 



by inflammation and caries of the navicular bone. In some instances 

 the disease undoubtedly begins in the bone, and the sesamoid sheath 

 becomes involved subsequently by an extension of the inflammatory 

 process. 



The thoroughbred horse is more commonly affected with the disease 

 than any other, yet no class or breed of horses is entirely exempt. The 

 mule, however, seems rarely, if ever, to suffer from it. For rea- 

 sons which will appear when considering the causes of the disease 

 the hind feet are not liable to be affected. As a general rule but one 

 fore-foot suffers from the disease, but if both should be attacked the 

 trouble has become chronic in the first before the second shows signs of 

 the disease. 



Causes. To understand fully how navicular disease may be caused 

 by conditions and usages common to nearly all animals, it is necessary 

 to recall the peculiar anatomy of the parts involved in the process and 

 the functions which they perform in locomotion. It must be remem- 

 bered that the fore-legs largely support the weight of the body when the ' 

 animal is at rest, and that the faster he moves the greater is the shock 

 which the fore-feet must sustain as the body is thrown forward upon 

 them by the propelling force of the hind-legs. This shock could not be 

 withstood by the tissues of the fore-feet and legs were it not that it is 

 largely dissipated by the elastic muscles which bind the shoulder to the 

 body, the ease with which the arm closes on the shoulder blade, and 

 the spring of the fetlock joint. 



But even these means are not sufficient within themselves to protect 

 the foot from injury, and so nature has further siipplemeuted them by 

 placing the coffin joint on the hind part of the coffin bone instead of di- 

 rectly on top of it, whereby a large part of the shock of locomotion is 

 dispersed before it can reach the vertical column, represented in the can- 

 non, knee and arm bones. A still further provision is made by placing 

 a soft, elastic pad (the frog and plantar cushion) at the heels to receive 

 the sesamoid expansion of the flexor tendon as it is forced downward 

 by the pressure of the coronet bone against the navicular. Extraordin- 

 ary as these means may appear for the destruction of shock, and ample 

 as they are when the animal is at a slow pace or unweighted by rider or 

 load, they fail to completely relieve the parts from concussion and ex- 

 cessive pressure whenever the opposite conditions are present. 



The result, then, is that the coronet bone forces the navicular hard 

 against the flexor tendon, which, in turn, presses firmly against the na- 



