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. 
Changes in the Internal Structwres.—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 
its 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- 
