160 
HISTOLOGY OF ANIMALS. 
those of the Ostrich , and it was then mentioned that 
the rich superficial network belonged to the sheath of 
the tendon, and not to the tendinous fibres them- 
selves. 
Whilst treating of articular cartilage, I may mention 
a peculiar deposit, as it is termed, which takes place in 
many joints that have been deprived of their cartilage 
by disease. The parts subjected to friction, in the move- 
ments of the joint, present a highly polished appear- 
ance, which is known as the ivory-like or 'porcellaneous 
deposit. If these specimens he examined, it will be 
found that all parts of the bone in the neighbourhood 
of the joint have an additional quantity of bony matter 
thrown out probably as the result of rheumatic inflam- 
mation. The same thing, no doubt, would have taken 
place upon the polished surfaces, had not the exuberant 
growth been kept down by the friction ; and, as no 
bone occupying this situation, unless of preternatural 
hardness, could receive such a polish, I was led to 
speculate on the cause of the appearance. I therefore 
removed slices, and rendered them sufficiently thin 
for microscopic observation, by grinding away the 
cut surface ; and, having examined them, I found that 
there was an almost total absence of the Haversian 
canals, whereby the bone was rendered exceedingly 
dense, and I concluded that the new osseous matter, 
having been prevented by friction from being thrown 
out upon the surface, was employed in filling up the 
canals, and by this means a substance, originally porous, 
