482 
NAVICULARTHR1TIS. 
interior. From absence of its accustomed impress of weight from 
above, by the force of which, in health, it is kept expanded, the hoof 
contracts, particularly at the heels and quarters ; and contracts, 
not only in its lateral but in its vertical diameter likewise, across 
from sole to wall : the lame foot becomes, in fact, altogether smaller 
than its fellow ; the difference in magnitude between the two fore 
feet, as the horse stands before his examiner, being now perfectly 
obvious ; and, moreover, the same is satisfactorily demonstrable 
by actual admeasurement. The shelving-in of the wall, and the 
concentric eminencies or rims upon it, are also now, generally 
speaking, strikingly conspicuous. There will likewise be felt 
some callous or osseous enlargement of the coronet and pastern, 
and perhaps of the cartilages at the heels as well ; it being about 
this period that ossific changes are commencing. 
At the time that the examiner, standing directly in front of the 
lame horse, is noticing these differences in the two fore hoofs, 
most likely his eye will be attracted upwards by the manifest 
flatness of surface, and apparent deficiency in substance, in the 
shoulder of the same limb, as compared with that of the sound 
one. So remarkable is this defalcation in cases in which pain 
and lameness have long been present, that, considering the ob- 
scurity in which the disease of the foot was years ago veiled, we 
cannot feel surprised that the shoulder should have been regarded 
as the actual seat of the lameness. We now, however, know 
better. We know that the shrinking or wasting away of the 
shoulder is but the natural consequence of lengthened Tepose 
of the part, or comparatively inadequate action of its muscles ; 
it being an established law in the animal economy that muscles be- 
come large and bulky in proportion as they are exerted, and vice 
versa. So that while the muscles of the lame limb are shrinking 
for want of action, those of the sound limb are actually swelling 
into larger size from having extra duty to perform : the circum- 
stance of the shoulder evincing this change more than any other 
part, and of one muscle in particular — the triceps extensor hrachii — 
striking our attention from its diminished bulk, arising simply from 
the shoulder being the most muscular part of the fore limb, and 
from that muscle being used in action, as well as standing, more 
than any other. Hence it happens that the fleshy prominence so 
conspicuous over the joint of the elbow in the sound limb is fre- 
quently hardly observable after long-continued lameness. 
Generally speaking, relapses of lameness, as I have had occasion 
before to remark, take place in the foot first attacked by navicular- 
thritis. Now and then, however, the opposite fore foot will become 
attacked, and the disease, returning first in one foot and then in the 
other, will exhibit a sort of gouty or metastatic character ; though 
