Inflammation of the synovial membranes, or synovitis, may affect the synovial sacs either of the joints or of the tendon sheaths. It may be acute or chronic and occur either idiopathically or follow the infliction of an injury. Its two chief forms are simple, or “closed,” synovitis and suppurative, or “open,” synovitis, the essential distinction between which is that in the latter microorganisms are present, whilst in simple synovitis they are absent. In all cases the disease is characterised by distension of the sac affected. Synovitis produced by a wound communicating with the outer air may be complicated by suppuration, and if the synovial membrane of a joint be involved the primary synovitis is almost always followed by traumatic arthritis. The commonest forms of chronic simple synovitis are:— INFLAMMATION OF THE PATELLAR SYNOVIAL CAPSULE. Inflammation of the synovial membrane of the femoro-patellar joint is most commonly seen in working oxen as a consequence of strains during draught. It is also found in young animals which have injured the synovial capsule through falls, slips, or over-extension of the limb. =Symptoms.= Development is slow and progressive, and injury may not be discovered until the lameness which follows has become fairly marked. This lesion is characterised by swelling in the region of the stifle. On palpation, fluctuation may readily be noted both on the outer and inner surfaces of the joint. The exudate is sometimes so abundant and distension so great that the straight ligaments, the neighbouring bony prominences, and the ends of the tendons are buried in the liquid swelling. Lameness, which is at first marked, often diminishes with exercise. The length of the step is lessened. =Diagnosis.= The diagnosis presents no difficulty, but the lesions must be distinguished from those due to tuberculosis in this region, rheumatic arthritis, and the specific arthritis seen in milch cows. =The prognosis= is grave, for the disease renders animals useless for work. =Treatment.= Rest, cold moist applications, and massage constitute the best treatment in the early stages. Should swelling persist, one may afterwards apply a smart blister or even tap the joint aseptically, drawing off the fluid and then applying the actual cautery. Irritant injections must be avoided. DISTENSION OF THE SYNOVIAL CAPSULE OF THE HOCK JOINT. _Bog Spavin in the Ox._ Bog spavin is frequent in working oxen and in oxen from three to five years old. It is due to strain in draught or to strain produced in rearing up at the moment of covering. Old bulls, heavy of body, and stiff in their limbs are predisposed to it.