644 THE HORSE. 
NAVICULAR DISEASE. 
THIS FORMIDABLE DISEASE, called also the navicular joint lameness, and 
navicularthritis, is the chief danger to be apprehended from a good- 
looking strong foot, just as the open flat one is prone to laminitis, and is 
rarely subject to disease in the navicular joint. The reason of this 
immunity on the one hand, and the contrary on the other, is this. The 
open foot, with a large spongy frog, exposes the navicular bone and the 
parts in contact with it to constant pressure in the stabie, so that these 
parts are always prepared for work. On the other hand, the concave sole 
and well-formed frog are raised from the ground by our unfortunate mode 
of shoeing, and when the whole foot is exposed to injury from battering, 
and in addition the tendon which plays over the navicular bone presses it 
against the os corone, the unprepared state in which this part is allowed 
to remain is sure to produce inflammation, if the work is carried far 
enough. Thus in each case the weak part suffers, but occasionally, though 
very rarely, the foot with an arched sole contracts laminitis, and the flat 
one is attacked by navicular disease ; the exceptions, however, are so few 
that they may be thrown out of the calculation, and from the shape of 
the foot alone it may almost invariably be pronounced, when a horse is 
known to be subject to chronic lameness, whether its seat is in the 
laminz or in the navicular joint. 
WHEN A FOOT IS EXAMINED AFTER DEATH which is known to have 
been the subject of navicular disease, the parts implicated are invariably 
either the navicular bone, or the soft parts in contact with it, or often all 
together. Most frequently on dividing the tendon of the flexor perforans 
and turning it down so as to expose the back of the joint between the 
navicular and coronal bones, that part will be greatly thickened and in- 
flamed, the tendon being often adherent to it. In the healthy condition 
Fie. 2.—ULCERATION OF THE POSTERIOR SURFACE OF THE NAVICULAR BONE. 
1. Lower or plantar surface of pedal bone. 2. Small specks of exostosis. 
3. Carious patch. 
there ought to be no adhesion of the fibres of the tendon to any part of 
the navicular bone but its postero-inferior edge, to which the tendon is 
fixed by some few fibres, the bulk passing on to be inserted in the os 
