STRUCTURE AND DEVELOPMENT OF BONE. 
119 
a deep rich brown colour, and as if possessed of a much higher degree of granularity 
than the surrounding parts. The cells of the tissue are not uncommonly surrounded 
by a similar granular condition of the matrix. This state of granularity is most con- 
spicuous near the bone, and less so near the cartilage, where the tissue becomes clear 
and transparent. The ossified cartilage is generally separated by a well-marked line 
from the subjacent bone. Exceptions to this, however, are not wanting, where the 
two pass, the one into the other, by insensible gradations. The bone at the line of 
junction is usually advanced into the ossified cartilage by rounded projections of 
variable size ; some of which reach nearly to the surface, while others are situated at 
some little depth. From this arrangement the articular bone is necessarily irregular 
in quantity. In one part it vvill dip to a considerable depth into the bone, while at 
another and perhaps contiguous part it will form but a thin layer. The external or 
articular surface is but slightly affected by the irregularities of the surface attached 
to the bone ; on the contrary, it presents an even surface, on which the articular car- 
tilage is placed in a uniform layer. 
The absence of Haversian canals, and the unfrequeney of lacunse with canaliculi in 
the articular bone, renders this tissue much less porous than ordinary bone, a condi- 
tion which probably contributes to its strength, and to the strength of the part in 
which it occurs. 
In the presence of this peculiar form of tissue at the articular extremities of bones 
we may perceive a striking instance of design. 
It would appear that the articular cartilage must rest upon a firm and uniform 
surface, otherwise it would, under pressure, yield unequally, and the joint would pro- 
bably be but imperfect in its action. Circumferential laminee are developed only on 
free surfaces, and do not present there a very level outer surface. A surface formed 
by Haversian systems wmuld be irregularly fluted or nodulated, like that beneath 
the calcified cartilage. Neither of those forms of development, then, would effect a 
condition of surface similar to that attained by the ossified cartilage. A careful con- 
sideration of the foregoing facts will, we think, lead to the conviction, that the 
presence of ossified cartilage as a basis for articular cartilage must not be regarded 
simply as the result of a slowly progressing ossification of a tissue prone to ossify ; 
neither must it be regarded as an imperfectly developed tissue in which the forma- 
tive process was arrested before the part had been perfected*; but it must be 
regarded as a constant element in the osseous system, having its special use, and 
necessary to the perfect organization of the skeleton in the higher forms of Verte- 
brata. 
Ossified Lacunal Cells . — In addition to the parts already described, tbe authors 
have found a condition of bone which has hitherto escaped observation, or if seen, 
has not been recognized as a form of osseous tissue. The bones of aged people 
not unfrequently become extremely light and spongy, readily break, and from the 
diminished amount of compact tissue, may in the case of the flat bones, such as 
* Kolliker, oper. cit. page 318, speaks of this tissue as imperfectly formed bone-substance. 
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