120 DISEASES OF THE HORSE'S FOOT 



navicular disease. More than probable it is that many 

 cases of so-called ' navicular ' have in reality been nothing 

 more than contraction brought about by one or other of the 

 causes we shall afterwards enumerate — cases where a due 

 attention to the prime cause of the mischief would, in all 

 likelihood, have remedied the lameness. 



Ckaiiges in the Internal Strnctaves. — It follows as a matter 

 of course that the changes we have described in the form of 

 the hoof itself carry with them alterations in the bones and 

 sensitive structures beneath it. The tissues, as a whole, 

 become atrophied. The os pedis becomes deformed, loses 

 iis circular shape, and gradually becomes more or less oval 

 in contour. At the same time, its structure becomes more 

 compact, the cribriform appearance of its anterior and 

 lateral faces more or less destroyed, and the few remaining 

 openings apparently increased in size. This atrophy of the 

 OS pedis is best noted at the wings. 



In the plantar cushion the effects of the atrophy are 

 noted in the smallness of the organ, in its becoming whiter 

 in colour than normal, and more resistant to pressure. 



The coronary cushion is also affected in the same 

 way, where the changes are noted most in its posterior 

 portions. 



A further effect of the narrowing of the heels, and their 

 consequent tendency to drop downwards, is the exertion of 

 a continual pressure on the sensitive sole. In course of 

 time, and especially in flat feet, this leads to the appear- 

 ance of corns. 



The navicular bone and bursa and the tendon of the 

 perforans also suffer from the effects of compression. The 

 movement of the tendon is restricted, and arterial supply to 

 the adjacent structures rendered deficient. The tissues of 

 the bone and bursa are insufficiently nourished, and the 

 secretion of synovia lessened. In this way it is conceivable 

 that navicular disease may follow the condition of simple 

 contracted heels. 



In common with the other structures, the lateral carti- 

 lages also suffer from the continual pressure. Their blood- 



