[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 exhausting calls made upon his system by the accompanying fever of the foregoing conditions, the case ends either in resolution or suppuration.  When suppuration occurs it is found, as a rule, at the sole, leading to almost entire separation of the sensitive and horny structures.  The pain, if possible, is even worse than in either of the foregoing stages, and relief for the suffering patient is only obtainable by the natural exit of the pus at the coronet, or by giving it escape with the knife at the sole.  As a rule, suppuration in laminitis is rare, and then only occurs when the disease has been of some several days’ duration.  It has been the author’s experience, however, to meet with it in a case but three days’ old.  This particular animal had laminitis restricted to the hind-feet.  The condition was diagnosed and pus liberated at the sole of one foot during the third day of the lameness.  The animal was cast on the fourth day, and pus obtained from the sole of the opposite foot.