NAVICULARTHR1TIS. 
247 
consists in the same pathological lesion as does navicularthritis : 
a fact that will serve to cast additional light on the etiology of both 
diseases. Still further light is derived from the superadded fact of 
the knee joint being occasionally affected with the same disease. 
In fine, there is no joint of the limbs, nor hardly any synovial 
structure in them, but what is liable to acquire, under fitting 
circumstances, a like disease. 
It will not appear strange that the navicular joints of the hind 
limbs should exhibit no such disease as so frequently invades the 
same joints in the fore limbs, when we come to consider the differ- 
ence of function, in progression, performed by the fore and hind 
extremities. While the former are little more than props of sup- 
port, and for that reason have their bones ranged in the form of 
uprjght columns, the latter have their bones obliquely placed, 
thereby constituting, one with the other, so many obtuse angles, to 
the end that by forming powerful levers, and affording every ad- 
vantage for action to the muscles attached to them, they may be 
fitted for the grand purpose of propulsion of the body onward. 
Any injury sustained in action by the upright column — the fore 
limb — will originate in jar or concussion, aggravated by the moving 
weight superimposed upon it ; whereas, any injury that may accrue 
to the hind limb will arise from the stress imposed upon the seve- 
ral levers and angles at the moment progression is being effectu- 
ated, the principal axis of which movement being the hock joint, 
that, as might be expected, will be the part to feel any inordinate 
weight or force of action. The navicular joint fails in the fore 
limb, then, simply from the circumstance of being the nethermost 
joint of the column — the last to receive the shock from above, the 
first from below; and the hock in the hind limb is the joint expected 
to fail, because it is not only situated so as to receive the brunt of 
the shock, which in the fore limb descends down the column, but 
has likewise, to sustain the weight of the body and its burthen, 
at the time force is employed in their impulsion onward, even 
while in state of motion. Joints appear to sustain more harm 
from shock or concussion, caused either by imposing great weight 
upon them while in action or by high or sudden descent of move- 
ment, than from hard or continued work ; and we shall universally 
find that those of the fore or hind extremity suffer most, in parti- 
cular the navicular or hock joints, according as they have respect- 
ively been the most called into action. We see this exemplified 
in hunters, racers, chargers, hackneys, carriage or coach horses, &c. 
It is an axiom in practice with every veterinarian of experience, 
that lameness in the fore limb has for its ordinary seat the foot , 
in the hind limb, the hock ; and, as we have seen, when we 
come to reason physiologically on the subject, science completely 
