weight
is placed upon the sole. Never intended to bear the strain thus imposed,
it naturally sinks. With the sinking is a corresponding 'dropping' of the
pedal bone--in fact, of the whole of the bony column. Seeing that the
structures _above_ the hoof are still normally adherent to the bones, it
follows that they must, as the os pedis sinks, be carried with it. As a
consequence we get a marked depression at the coronet (see Fig. 117, _a_),
which depression may be often noticed after the second or third week of a
severe attack of the disease.

[Illustration: FIG. 116.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF
EIGHT DAYS' STANDING. The separation between the sensitive structures and
the hoof is indicated by a dark line. The cavity is filled with exudate. It
will be noted that as yet there is little change in the position of the os
pedis.]

Here, again, though to a greater extent than that caused by the haemorrhage
alone, the os pedis appears to be pushed backwards, the space at the toe
between the bone and the horny box being closely filled with the yellow,
slightly blood-stained exudate. This condition is well depicted in Fig.
117.

[Illustration: FIG. 117.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF
FOURTEEN DAYS' STANDING. _a_, The depression at the coronet caused by the
dropping of the bony column within the horny-box: _b_, a portion of the
sensitive sole pushed downwards and forwards by the descending os pedis.]

With the descent of the os pedis we get in many cases a penetration of the
horny sole (see Fig. 117), leading always to serious displacement of the
sensitive sole (see Fig. 117, _b_), and often to caries of the exposed
bone.

The backward displacement of the os pedis may be accounted for in two ways.
Firstly, the greater vascularity of the membrane covering its front leads
to a greater outpouring of inflammatory fluid in that particular position.
Here, therefore, loss of adhesion with the wall is greatest, while into the
cavity so formed is poured a large quantity of a fluid that is practically
incompressible. The os pedis _must_ be pushed backwards. Secondly, the
manner in which the animal distributes his weight--namely, upon the
heels--is calculated to aid in the bone's backward movement, for with his
feet in this position tension upon the extensor pedis is relaxed, while
that upon the flexor perforans is greatly increased.

(c) _Suppuration_.--Should the animal survive the pain and exh