AN ESSAY ON CHRONTC PODOTROCHOLITIS. 
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tions devolving upon the trochlea of the foot, as well as the various 
kinds of contraction which may impede those functions by pressure 
from below. 
In the action of the horse, the navicular bone rises and descends 
upon the perforans tendon, at the same time that it is forcibly 
pressed against this tendon. Nature has contrived a secretory 
membrane for the constant lubrification of these two fricating bodies, 
and has thus prevented the injurious effects so likely to arise from 
the continual friction going on between them ; but if, from any 
cause whatsoever, this friction becomes too great, nature is no 
longer able to prevent the parts from changing their physiological 
state. I saw in a horse of the Lithuanian breed, so oblique upon 
his pasterns that at each step the fetlock touched the ground, an 
entire detachment of the fibres from the anterior surface of the 
flexor tendon, opposite to the sesamoids. This morbid altera- 
tion, identical with that observable in podotrocholitis, evidently 
arose from the position of the inferior joints of the limbs, and the 
excessive friction of the tendon against the bone. If the gliding 
of the tendons over the trochlese of the hind legs be not attended 
with similar effects, it is attributable to the circumstance of the 
friction being considerably less, as well as to the weight being more 
supported by the upper joints of these limbs. The structure of the 
fore and hind extremities being different, they have different func- 
tions to fulfil. 
The posterior limbs are the actual locomotive agents of the body ; 
the anterior limbs are but its supporters: hence their structure must 
be based upon different principles. To the hinder legs belong elas- 
ticity and propulsive power; to the fore, resistance. Nature has 
attained her aim by making the former like a grasshopper spring, 
and assimilating the latter to a column. 
If we examine the posterior extremities, from the quarter to the 
pastern, we shall find that, whether at rest or in action, the bones 
are united, two and two, by their articulatory ends meeting and 
forming angles, the sines of which are greater or less according to 
their conformation. The pelvis forms an angle with the femur, 
the summit of which is directed backwards; the femur forms 
another angle with the tibia, in an opposite direction to the former; 
and the tibia again, by its union with the tarsus and metatarsus, 
produces an angle which extends from before backwards. All 
these angular flexuosities are permanent; they never become 
straightened even when the horse rests his whole weight upon one 
limb ; the opposition of the flexors and extensors constantly main- 
tains a more or less perfect equilibrium. This disposition may be 
regarded as a spring composed of a succession of pieces, whose 
elasticity resides in the muscular apparatus : hence it results that 
