70 
LAMENESS IN HORSES. 
hock joints are the suffering parts, under like circumstances, in the 
hind limbs. Considerations of the structure of the hock joint, of 
its situation in the animal frame, of its motions and functions, will 
satisfactorily account for its susceptibility to derangement and dis¬ 
ease, as compared with other joints of the hind limb ; and we shall 
pretty invariably find that its disorders are prevalent and intense, 
according as the animal has been over-worked or over-weighted 
at a tender age, or excessively worked or anywise abused in work 
at an adult or advanced period of life. Intensity of motion, or 
any undue stress upon the joint of the hock, tends to create irritation, 
if not inflammation, in a part so delicate by nature as its lining 
membrane, the consequence of which is augmented secretion of 
synovia, producing what we call “bog spavin.” Young horses with 
large joints put to do work or carry weight beyond their strength ; 
heavy-worked harness horses, hunters, steeple-chace horses, racers, 
and so forth, are on these accounts the especial subjects of bog 
spavin. And those equestrian movements that throw most stress 
upon the hocks, such as pulling horses upon their haunches, back¬ 
ing them, suddenly or violently checking or pulling them up, heavy 
draft, &c., will operate in a peculiar manner in the production of 
the disease. 
Between the Pathology of Bog Spavin and Windgall 
there is this important difference—that, while windgall has a bursa 
for its seat, bog spavin consists in enlargement and saccular dila¬ 
tation of the capsule of the joint itself, viz. the joint of the hock. 
It will be remembered that the hock is composed of several joints or 
articulations; but that the principal of these is the one between the 
tibia and astragalus, which, in consequence of its being that through 
which the motion requisite for progression is mainly carried on, 
commonly goes by the appellation of the hock joint; and this joint 
it is which is the seat of bog spavin. Inordinate stress or motion 
of this joint, as has been already observed, has a tendency to pro¬ 
duce irritation of its delicate lining membrane; and this, once set 
up, is productive of augmented synovial secretion in it: the effect 
of which is, first, distention, and subsequently dilatation, of the 
capsule of the joint. In place of from three drachms to half an 
ounce of synovia, which is the quantity usually found in the joint, 
in this anormal condition of it from two to three ounces, and even 
more, will frequently be found to be collected : in fact, the joint 
may truly be declared to be in a dropsical state. Under such in¬ 
creased pressure the capsule of the joint gives way ; and those 
parts of it which are weakest from want of support externally give 
way the soonest, or in other words bulge, and form tumours visible 
through the skin. The part of the capsule the most likely to bulge, 
not only from its being a part embraced by ligament or tendon, 
