Callous Tumour. 391 
zation of the tumour was shewn by the pre- 
sence of spots, of a redder colour, inter- 
spersed through its substance. 
In these dissections we find perfect actions 
of the external membrane, the fracture is 
therefore enveloped in a tumour clearly a pro- 
duction of that part; but the actions of the 
internal membrane are deficient, and hence a 
portion of the face of the fracture is uncover- 
ed ; the denuded part is found projecting into 
a cavity formed in the tumour, which is filled 
with a smooth slippery fluid. In cases of un- 
united fracture, tumour will be found in those 
cases where the want of union depends sim- 
ply upon deficient actions of the internal 
membrane; it will be absent where the want 
of union is caused by disease of the external 
membrane. By considering the above dissec- 
tions, we become able to explain the forma- 
tion of that very curious circumstance, the 
artificial joint, (a rare case, but of which 
several are upon record,) and to ascribe it to 
deficient action of the internal membrane, 
whilst the outer membrane performs its func- 
tion duly. In the artificial joint the secon- 
dary effusion in its progress to organization, 
beomes converted into a capsular ligament; 
the fractured faces, partially uncovered by 
effusion from the inner membrane, project 
