204 NOTES OF THE EXAMINATION OF 
the epiphysis and the cartilage which separated it from the shaft. Indeed, the 
resemblance between the two objects was exceedingly close, for the disposition 
of the cartilage cells in piles perpendicular to the surface of ossification, while 
present in the shaft of the metatarsal bone, was absent alike in the epiphysis, 
and in the exostosis; also the part of the cartilage that was immediately con- 
tiguous to the newly formed bone of the epiphysis was evidently calcified, and 
closely resembled the calcified cartilage of the exostosis, both in the condition 
of the cells and in the eroded form of its margin; the eroded edge, again, was 
almost universally lined with a layer of true bone exactly as in the exostosis, 
except that the layer was generally somewhat thicker. 
These facts appeared at first inconsistent with the idea of the layer of true 
bone having been deposited subsequently to the formation of the excavations, 
for that supposition implied that both in the epiphysis and in the exostosis, 
the process of excavation of the calcified cartilage had almost entirely ceased, 
or, in other words, that the conversion of the calcified cartilage into true bone 
was almost or altogether suspended; and this appeared particularly unlikely 
in the case of the exostosis, which was known to have been growing rapidly 
before its removal. 
The examination of the ossifying epiphysis of one of the bones of a calf’s 
foot has, however, convinced me that the layer of true bone is deposited on 
the walls of previously existing excavations. The cells of the calcified cartilage 
are there seen to enlarge at the expense of the matrix as they approach the 
cancellous structure of the epiphysis, and at the same time to acquire a granular 
appearance, just like that of the rudimentary medullary substance with which 
the last formed areolae are filled; and finally, they evidently form by their 
coalescence the excavations in the margin of the calcified cartilage. Those 
parts of these excavations or areolae which are farthest from the perfect bone, 
and which have been last formed, are devoid of any osseous lining; but at 
a very short distance from their extremities they acquire upon their surface 
a thin layer of lacunated bone, which is seen to increase gradually in thickness 
at the expense of the cavities as they are traced nearer to the perfect bone. 
A further examination of the exostosis also showed that in some parts the 
osseous lining of the margin of the calcified cartilage was absent, while, on the 
other hand, there appeared at these parts evidence of a change in the deepest 
cells of the calcified cartilage, like that observed in the calf’s foot, viz. an en- 
largement of the cells, and a conversion of their contents into a granular sub- 
stance previous to their coalescence to form the excavations. 
It thus appears that the process by which the calcified cartilage of the 
exostosis was converted into the cancellous structure of the interior, is essentially 
