NINTH ANNUAL YEAR BOOK— PART X 439 
the navicular. Extraordinary as these means may appear for the des- 
truction of shock, and ample as they are when the animal is at a slow 
pace or unweighted by rider or load, they fail to relieve completely the 
parts from concussion and excessive pressure whenever the opposite con- 
ditions 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 navicular as the force of the contracting muscles lifts 
the tendon into place. It is self-evident, then, that the more rapid the 
pace and the greater the load, the greater must these contending forces 
be, and the greater the liability to injury. For the same reason horses 
with excessive knee action are more likely to suffer from this disease 
than others, concussion of the foot and intense pressure on the tendon 
being common among such horses. ~" 
Besides the above exciting causes must le considered those which pre- 
dispose to the disease. • Most prominent among these is heredity. It 
may be claimed, however, that an inherited predisposition to navicular 
disease consists not so much in a special susceptibility of the tissues 
which are involved in the process as in a vice of conformation which, as 
is well known, is likely to be transmitted from parent to offspring. The 
faults of conformation most likely to be followed by the development of 
navicular disease are an insufficient planter cushion, a small frog, high 
heels, excessive knee action, and contracted heels. Finally, the environ- 
ments of domestication and use, such as dry stables, heavy pulling, bad 
shoeing, punctured wounds, etc., all have their influence in developing 
this disease. 
Symptoms. — In the early stages of navicular disease the symptoms are 
generally very obscure. When the disease begins in inflammation of the 
navicular bone, the animal while at rest points the affected foot a time 
before any lameness is seen. While at Vvork he apparently travels as 
well as ever, but when placed in the stable one foot is set out in front 
of the other, resting on the toe, with fetlock and knee flexed. After a 
time, if the case is closely watched, the animal takes a few lame steps 
while at work, but the lameness disappears as suddenly as it came, and 
the driver doubts if the animal was really lame at all. Later on the 
patient has a lame spell which may last during a greater part of the day, 
but the next morning it is gone; he leaves the stable all right, but goes 
lame again during the day. In time he has a severe attack of lameness, 
which may last for a week or more, when a remission takes place and it 
may be weeks or months before another attack supervenes. Finally, he 
becomes constantly lame, and the more he is used the greater the lame- 
ness. 
In the lameness from navicular disease the affected leg always takes 
a short step, and the toe of the foot first strikes the ground; so the shoe 
is most worn at this point. If the patient is made to move backward, 
the foot is set down with exceeding great care, and the weight rests upon 
the affected leg but a moment. When exercised he often stumbles, and 
if the road is rough he may fall on his knees. If he is lame in both 
feet the gait is stilty, the shoulders seem stiff, and, if made to work, 
sweats profusely from intense pain. Early in the development of the 
