e reasons
for these positions being so affected we shall deal with when treating of
the causes of sand-crack in general. It is interesting to note that the
portions of wall known as inside and outside toe are seldom affected.

_(b) Their Length_.--_Complete_ when they extend from the coronary margin
of the wall to its wearing edge; _Incomplete_ when not so extensive.

_(c) Their Severity_.--_Simple_ when they occur in the horn only, and do
not implicate the sensitive structures beneath; _Complicated_ when
deep enough to allow of laceration and subsequent inflammation of
the keratogenous membrane. Such complications may vary from a simple
inflammation set up by laceration and irritation of the sensitive
structures by particles of dirt and grit that have gained entrance through
the crack, to other and more serious changes in the shape of the formation
of pus, haemorrhage from the laminal vessels, caries of the os pedis, or the
development of a tumour-like growth of horn on the inner surface of the
wall known as a keraphyllocele.

_(d) Their Duration_.--_Recent_ when newly formed; _old_ when of long
standing.

_(e) Their Starting-point_.--This last distinction we make ourselves,
and, referring to cracks of the wall, term them _high_ when commencing from
the coronary margin, _low_ when starting from the bearing surface.

_Causes_.--We have already classified sand-crack as a disease arising from
faulty conformation. Thus, in just so far as a predisposing build of body
may be handed down from parent to offspring, we may regard sand-crack as
hereditary. If we do so, however, we must afterwards make up our minds
to sharply distinguish between the sand-crack plainly brought about by
accidental cause, and that occurring as a result of hereditary evil
conformation.

With regard to the latter, we need hardly say that feet with abnormally
brittle horn are extremely liable. But with this, as with many other
affections of the feet, we shall find it necessary to consider several
causes acting in cooperation. In this case, for instance, given the brittle
horn, it becomes necessary to further look for exciting causes of its
fracture.

We will take conformation first. In the animal with turned-out toes a more
than fair share of the body-weight is imposed on the horn of the inner
quarter. Here, then, three causes exert their influence together: The horn
is brittle; the wall of the inner quarter is thinner than that of the
outer; ad