’The post-mortem inspection revealed a complete fracture of nearly the whole of the articulating surface and the left wing of the pedal bone (as shown in Fig. 160).’[A]

[Footnote A:  J. Freeman, M.R.C.V.S., Veterinary Journal, vol. xxxi., p. 324.]

4.  A further interesting case is reported by Mr. William Hurrell.[A] Here the cause was presumably galloping in the field, for the subject, a cart mare running out at grass with her foal, was suddenly found to be lame.

[Footnote A:  Ibid., vol. v., p. 408.]

As the lameness continued to increase in severity, Mr. Hurrell was called in on August 1, and diagnosed the case as one of foot lameness.  On this date the foot was pared out, and a large accumulation of pus discovered, Poulticing and antiseptic dressings were continued until August 16, when a movable piece of the os pedis was found at the toe.

On August 25 this detached portion of the bone was removed, and turned out to be the whole of the anterior margin of the os pedis, measuring 3-1/2 inches long, and varying in width from 1/2 inch to 1-1/2 inches.  On September 20 the mare was working without lameness.

3.  FRACTURES OF THE NAVICULAR BONE.

Hidden within the wings of the os pedis, and protected as it is by its tendinous covering and the yielding substance of the plantar cushion, the navicular bone is even less liable to fracture than either of the other bones of the foot.

The most common cause of fracture of the navicular is that of stabs or deep pricks in the region of the point of the frog (see p. 216).  Following that, the next most common cause is violent injury.  We thus find the navicular bone fractured, together with one or both of the other bones of the foot, when the foot is run over by a heavy vehicle.  One such case is reported by Mr. J.H.  Carter, F.R.C.V.S., where the horse’s foot was run over by a tram-engine, in which the os pedis and the navicular were fractured in several places.[A] A further case is on record where a sharp blow on the front of the hoof was the cause.  In this case the os pedis and other structures were uninjured, but the navicular bone was fractured into three large, and about half a dozen small, pieces.[B]

[Footnote A:  Veterinary Journal, vol. xxxi., p. 246.]

[Footnote B:  Veterinarian for 1857, p. 73.]

Fractures of the navicular may occur, however, in which history of a prick or of a violent injury is absent.  See reported case below.

As with fractures of the os pedis and the os coronae, so with this exact diagnosis is difficult—­we may say almost impossible.  With a history of violent injury, however, some little regard may be paid to a continued heat and tenderness of the foot, and a distinct inclination on the part of the animal to go on the toe.  Even when the fracture is the result of a prick, and the bone is plainly felt with the probe, we still cannot be positive as to fracture.