Symptoms and Diagnosis.—­Acute synovitis of a joint leads to heat of the parts, pain, distension of the capsule, and, where the joint may be easily felt, fluctuation.  In the articulation with which we are dealing, however, these last two symptoms are not easily detected, for the surrounding structures—­namely, the lateral and other ligaments of the joint, the extensor pedis tendon in front, and the perforans behind, together with the dense and comparatively unyielding nature of the skin of the parts—­are such as to prevent distension and fluctuation becoming marked to a visible extent.  We are able to diagnose the case as one of foot lameness, and, with a history of a severe blow or other injury, are able to assume that this condition, perhaps attended with periostitis, is in existence.

When other symptoms present themselves diagnosis may be more certain.  The animal becomes slightly fevered, throbbing pains in the joint manifest themselves by irregular pawing movements on the part of the patient.  The animal comes out from the stable stiff, even dead-lame, and the limb is carried with the lower joints semiflexed.  The breathing is hurried and the pulse firm and frequent, while in a bad case patchy perspiration breaks out at intervals on various parts of the body.  If with this we get a puffy and tender swelling in the hollow of the heel, our diagnosis may be certain at any rate as to the existence of joint trouble, although, from reasons we have given, we may not be able to mark its exact nature.

2. Chronic.—­Simple synovitis may in many instances become chronic.  In this case we have simply a pouring into the synovial capsule of serous fluid, and with it an increased quantity of synovia—­this time with an absence of the usual inflammatory phenomena.  Beyond the swelling of the capsule there is little to be noticed.  The joint becomes perhaps a little weaker, but pain or tenderness and heat are entirely absent.  Such a condition, by reason of the natural rigidity of the parts, is not to be observed in the foot, although at times it must most certainly occur.  Examples of such a condition are to be found in bog-spavin, in hygroma of the stifle, and sometimes in the fetlock.  From a study of these, we know that they may be induced by frequent attacks of acute synovitis, from repeated slight injuries or bruises, or from strains to the ligaments of the joint; or that they may be chronic from the outset.  We know, too, that in such cases the synovial membrane becomes thickened, and that in places it may have extended somewhat over the edges of the articular cartilages.  It is only fair to suppose that such changes occur also in the pedal articulation.  In that case we may take it for certain that the natural rigidity of the surrounding structures has the effect of pushing the thickened membrane further between the bones of the joint than occurs in a like condition elsewhere, leading, of course, to a lameness that is marked in degree but occult as to cause.