CURB. 
743 
easy, then, to estimate the great strains to which this ligament is subject, 
and to understand why it frequently becomes strained. Horses with 
tied-in and “ sickle-shaped ” hocks are especially predisposed to 
curb, and, if incautiously worked when young, generally develop it. 
.Che reason appears to be that, as the calcano-cuboid ligament serves 
to unite the metatarsus to the os calcis, and as the calcis acts like a 
lever, to the end of which are attached the extensor tendons, especially 
the tendon of the gastrocnemius, the more nearly the bend of the hock 
approaches a right angle, the more powerfully does the gastrocnemius act, 
and, consequently, the more likely is this ligament to become strained. 
In “tied-in” hocks the lower row of bones and 
the upper end of the metatarsus are too slight; the 
distance between the calcano-cuboid ligament and 
the anterior margin of the hock, which represents 
another lever, is too short. The less this distance, 
the more liable is the ligament to be strained and 
inflamed when the limb is forcibly extended during 
movement. 
The external causes consist in severe exertion 
violent attempts at extension at moments when the 
limb is flexed and sustaining weight, as in jumping, 
or in heavy or uphill draught-work. Curb some¬ 
times results from the horse being suddenly thrown 
on its haunches. The more powerful the muscles 
of the quarter and limb, the greater the strain on 
the calcano-cuboid ligament, a fact which explains 
the frequency of curb in very powerful horses. 
Curb sometimes occurs as a complication of spavin, 
in consequence of inflammation extending to the 
back of the joint and to the calcano-cuboid liga¬ 
ment. This is the cause of the so-called bony curb, which, however, 
might better be included under the term spavin. 
Symptoms. (1) Change in the form of the joint. Curb appears as a 
swelling in the otherwise straight line of the hock when seen from the 
side (fig. 275). Careful examination and palpation differentiate strain of 
the calcano-cuboid ligament from disease of the tendons, tendon sheaths, 
or skin. It is more difficult to distinguish between bony curb and strain 
of the ligament, though in the former additional exostoses usually exist 
on the inner side of the joint. 
(2) Lameness is comparatively rare in curb, which in working-horses, 
therefore, forms little more than a blemish. Lameness, when occurring, 
is either due to the accompanying spavin, or is caused by inflammation 
in the calcano-cuboid ligament. This explains why it so often resembles 
