Williams, Fisher, and Udall: The Spavin Group. 9 
It is most apparent when the intense areas of the disease 
involve an important articulation. The character of this synovitis 
has been in controversy. Many of the older authors speak of 
this affection in a general way as arthritis sicca or dry arthritis, 
but, when they do so, they have in mind, apparently, only those 
joints of limited motion and scant synovia. It is essential for 
repair in cases of developed spavin or ringbone that eventually 
synovia should cease to be secreted in order that contact’ of 
the denuded bones may occur and permit anchylosis. In these 
articulation there are only very limited synovial sacs incapable 
of distension, and severe inflammation apparently quickly des- 
troys, or diminishes, their secretory power. In the larger artic- 
ulations with extensive synovial sacs, the secretion -becomes 
very greatly increased. In many cases of spavin, presumably 
without erosion of the cartilage of the tibio-astragaloid articu- 
lation, the synovial sac of this joint is greatly distended, con- 
stituting what we may well term a false bog spavin in contra- 
distinction to the generally greater distension of the joint, some- 
times unaccompanied by lameness, or, so far as we know, by 
any osseous disease, to which we ordinarily apply the term of 
bog spavin. Ths distension serves to cover and disguise the 
exostosis of spavin and in this way tends to lead to error in 
diagnosis. It is a part of the one affection, the synovitis of ordi- 
nary spavin having the same etiology and prognosis. 
+ Still more pronounced, and quite characteristic of the malady, 
is the synovitis in gonitis. There the distension of the femoro- 
patellar bursa is, next to the lameness, the most prominent 
sign of the malady and, moreover, its results are serious for 
the integrity of the articulation. When occurring in young 
animals, the extreme distension of this sac lifts the patella 
upwards and forwards, until it is above the external trochlear 
ridge, inducing a floating dislocation of the patella, as seen in 
Figs. VIII and IX. The floating patella is drawn outwards 
over the external ridge by the biceps femoris and other muscles 
during flexion, and inwards again during extension, the result- 
ing attrition wearing away the cartilage and bone from the 
summit of the external trochlear ridge and from the median 
ridge of the patella, as shown at E and E* in Fig. VII. 
The increased pressure upon the summit of the ridge, the 
disuse of the trochlear groove and the internal ridge, along 
with the disease processes, taking place within the articular 
2 
