THE NAVICULAR-JOINT DISEASE 139 



as it is very common for low, unprincipled dealers 

 to cover over sand-cracks so neatly with pitch, and 

 afterwards along the whole hoof, that it is so com- 

 pletely concealed, as not to be observable except by 

 a narrow inspection. 



THE NAVICULAR-JOINT DISEASE. 



Behind and beneath the lower pastern-bone, and 

 behind and above the heel of the coffin-bone, is 

 placed a small bone, called the navicular bone. 

 (See Plate vi, fig. 10, e.) The use of this bone is to 

 support and strengthen the union between the 

 lower pastern and the coffin-bone, and to assist the 

 flexor tendon in its action as it passes over it, in 

 order to be inserted into the bottom of the coffin-bone, 

 and forms a sort of joint with that tendon. The 

 navicular bone is subjected to much pressure, as is 

 also this tendon ; and besides, there is much play 

 between them in the bending and extension of the 

 pasterns. 



CAUSE. Like many other complaints of the 

 horse, this is often induced by sudden and 

 violent exercise after the animal has been allowed 

 to stand in the stable inactive. The parts not 

 being for some time adapted to overstrained action, 

 there may be too much play between the bone and 

 the tendon, and by concussion of the parts the 

 synovial membrane which covers the tendon and 

 forms the bursae may be bruised ; or the cartilage 

 of the bone may be inflamed, and thus produce 

 destruction of it, and cause a lameness of the most 

 painful description. From the navicular bone being 

 so obscurely situated, it is difficult to ascertain by 

 inspection when it is diseased. And this has 

 puzzled many to find out the cause of lameness 



