n width occurring at the posterior part of
the foot without destroying the union of the two set of leaves.
Further, by their connection with the vascular system of the foot,
their elastic movements materially assist the circulation. The
primary use of the lateral cartilages is to render the internal
foot elastic, and admit of its change in shape which occurs under
the influence of the weight of the body. The alteration in the
shape of the foot is brought about by pressure on the pad, which
widens and in consequence presses on the bars. The pressure
received by the pad is also transmitted to the plantar cushion,
which likewise flattens and spreads under pressure. Both of these
factors force the cartilages slightly outwards. When the posterior
wall recoils the cartilages are carried back to their original
position. Should the elastic cartilage under pathological
conditions become converted into bone, its functions are destroyed,
and lameness may occur.

Etiology and Occurrence.--The causes of ossification of these
cartilages are several. No doubt there exists a predisposition to this
condition for it is of such frequent occurrence in heavy draft types of
horses. Concussion plays an important role and, according to
Moeller's[28] theory, which is sound, high heel calks prevent the frog
from contacting the ground, and as weight is placed upon the foot "the
lateral cartilages are subjected to a continuous inward and downward
dragging strain."

[Illustration: Fig. 31--Ringbone and sidebone.]

The condition affects the cartilages of the fore feet more frequently
than those of the hind and the outer cartilage is more often ossified
than is the inner. This fact may be accounted for by its more exposed
position; it is also frequently injured by being trampled upon and
otherwise contused or cut, as in lacerated wounds of the quarter.

Symptomatology.--Ossification of the cartilages is known by grasping
the free borders with the fingers and attempting their flexion; the
rigid inflexible ossified cartilage is thus easily recognized.

Lameness during weight-bearing occurs in the majority of cases at some
time. Much depends on the conformation of the foot and whether the
involvement affects one or both cartilages as to the degree and duration
of lameness which marks this affection. In narrow and contracted heels
it is reasonable to expect more lameness than