nd may be
regarded as the direct continuation of the plantar. At the fetlock it is
placed immediately above the digital artery, but afterwards takes up a
position directly behind that vessel. Together with the digital artery it
descends to near the basilar process of the os pedis. Here it passes with
the plantar artery into the interior of the os pedis, and continues its
main branch, with the preplantar artery, in the fissure of the same name,
to finally furnish supply to the os pedis and the sensitive laminae. It is
this nerve which is divided in the low operation of neurectomy.

Beyond the fact of this branch descending, in the region of the pastern, 1
inch behind the digital artery, a further point of interest presents itself
to the surgeon, and one to which attention must be paid. This is the
presence in close proximity to the nerve of the Ligament of the Pad
(Percival), or the Ligament of the Ergot (McFadyean). This is a
subcutaneous glistening cord originating in the ergot of the fetlock,
passing in an oblique direction downwards and forwards, and crossing over
on its way both the digital artery and the posterior branch of the digital
nerve.

In the foregoing description of the anatomy, we have taken the fore-limb as
our guide. In the hind-limb, where they reach the foot, the counterparts of
the tendons, arteries, veins, and nerves differ in no great essential from
their fellows in the fore. They will therefore need no special mention.

G. THE COMPLEMENTARY APPARATUS OF THE OS PEDIS.

This consists of two lateral pieces, the LATERAL CARTILAGES or
_Fibro-cartilages_ of the pedal bone, united behind and below by the
_Plantar Cushion_.

1. THE LATERAL CARTILAGES.--Each is a flattened plate of cartilage,
possessing two faces and four borders separated by four angles.

The external face is convex, covered by a plexus of veins, and slightly
overhangs the pedal bone. The internal face is concave, and covers in
front the pedal articulation and the synovial sac, already mentioned as
protruding between the antero- and postero-lateral ligaments of that joint.
We have already remarked that this is a point of interest to be remembered
in connection with the operation for quittor. Below and behind, the
internal face of the cartilage is united to the plantar cushion.

[Illustration: FIG. 16.--EXTERNAL FACE OF THE OUTER LATERAL CARTILAGE. 1,
External face of cartilage--(_a_) its upper border, (_b_) its posterior
border,