8 Williams, Fisher, and Udall: The Spavin Group. 
being irregularly conical, the projections from the two opposing 
surfaces alternating and interlocking in a way. to produce 4 
false anchylosis competent to fix the joint to a limited degree 
without giving the security of a true and complete fusion. 
PERIOSTITIS AND ExostosEs. As we have already ‘suggested, 
the ostitis is general, with here and there points of special 
virulence which determine gross lesions. These areas of inten- 
sity are not always subchondral, but are possibly even more 
frequently subperiosteal, leading to the formation of exostoses, 
which constitute the most universally visible lesions of the 
malady. 
In many cases the subchondral and subperiosteal lesions 
are simultaneous, as is shown in Fig. V, where the destruction 
of the articular cartilage and the exostoses are equally prominent. 
In other cases, as seen in many peri-articular ringbones (Fig. 
VI), the areas of intensity are chiefly subperiosteal and the 
articular cartilage largely escapes destruction. When the in- 
flammation involves the periosteum, it is generally in the 
immediate vicinity of the attachments of the capsular ligaments. 
Instead of the destructive processes, we have outlined in 
the osseous tissue, the periosteum, when the seat of the disease, 
tends to a productive inflammation. The deeper osteogenetic 
layer assumes increased activity, the osteoblasts multiply, and 
new osseous tissue is rapidly formed. The Haversian canals 
extend outward from the normal into the new formed bone. 
The new osseous tissue possesses all the essential characters 
of normal bone, but the regularity is disturbed in various ways. 
The Haversian canals are larger and more irregular in arrange- 
ment, the new bone is softer and more fragile. Its outline dur- 
ing life appears somewhat smooth and regular, but when the 
affected bones are macerated and the connective tissue removed, 
the surface is found to be very irregular with many deep inden- 
tations passing into the exostoses, dividing them up into irreg- 
ular adherent bony masses. The new formed bone tends finally 
to undergo osteo-sclerosis when the active stage of the disease 
has passed, and may in time atrophy. 
SyNovitis. Synovitis is a well-nigh constant condition in 
this affection, and while it apparently bears a close relation in- 
many cases to the usury of the articular cartilage, this does 
not seem to be constant, nor can synovitis be recognized in all 
cases, either inira vitam or post mortem. 
