Callous Tumour. 295 
these parts becoming the bed of an earthy 
deposition, hence arises a necessity for the 
formation of a covering to the callous tumour 
which shall ultimately become the true exter- 
nal periosteum. This membranous covering 
first appears about the thirteenth day ; most 
observable where the extreme bounds of the 
tumour terminate upon the sound periosteum ; 
hence we naturally conclude it to be a pro- 
duction or prolongation of that part of the 
membrane, and nota condensation of the cel- 
lular membrane, as isthe case with the cover- 
ing of many unnatural tumours. On the fif- 
teenth day the tumour is wholly covered by 
an extension of the. periosteum, and is per- 
fectly defined. On the nineteenth day seve- 
ral large blood vessels are found ramifying 
upon this membrane ; the tumour is very vas- 
cular and the pervasion and union of all parts 
by blood vessels is complete. 
From this period the tumour gradually di- 
minishes in size, and becomes more and ‘more 
consolidated as it approaches the structure of 
solid bone. Into this process of earthy depo- 
sition as into the pervasion of the tumour by 
blood vessels, it forms no part of my subject 
to enquire; nothing more is necessary to a 
completion of reunion than a’continuance of 
actions now in full operation, viz. the absorp- 
