STRUCTURE AND DEVELOPMENT OF BONE. 
Ill 
oval or circular outline, and that the walls of such canals have a tolerably uniform 
surface. When examining sections of bone it is necessary to bear this fact in mind, 
for on a close inspection it will be seen that there are other spaces which possess a 
different character, although up to the present time, so far as the authors know, this 
difference has not been recognized. 
These spaces are irregular in shape, and have an irregular, festooned and often 
jagged outline, similar to that found on the surface of bone which has been removed 
by exfoliation, similar also to the surface left upon the fang of a tooth after a part has 
been absorbed. Such spaces correspond in shape to the peripheral outline of one or 
more of the Haversian systems, and are in fact subservient to the development of 
those systems, and necessarily precede their formation (Plate VI. figs. 2 a, 3 a, 4 a). It 
is proposed to call these spaces which are produced by absorption, Haversian spaces, 
as this name is indicative of their ultimate connection with the Haversian systems. 
In the Haversian canals we have surrounding laminae, but in the spaces the boun- 
daries are formed by portions of several systems, each of which has been in part 
removed in the formation of the spaces, as shown in figures 2 and 3, and Plate V., 
which, on being compared with figure 1, will illustrate the difference between the 
spaces and canals ; allowance must, however, be made for the difference of size, as 
in figure 1 the parts are less magnified than in the other illustrations. In newly- 
formed bone situated near ossifying cartilage, the Haversian spaces are exceedingly 
numerous and large, frequently affording room for the development of two or more 
systems (fig. 5, Plate VI. fig. 24, Plate VIII.), while in older bone they are far less 
numerous, and generally less in size. In no case, however, are they wholly absent. 
They are found even in the bones of old subjects, and in connection with them newly 
developed systems. 
This is a very important fact, as it demonstrates that the old tissue is removed in 
masses, and a new one developed in its place. It has long been taught that the 
older particles of an internal tissue are removed by absorption and new ones substi- 
tuted, and this throughout the life of the individual. But the authors believe that 
they have demonstrated it for the first time. 
On examining with care a series of sections, the Haversian spaces will be found in 
various conditions. In one place the space will have attained a large size, while in 
another part of the same section its commencement will be seen extending from one 
side of an Haversian canal. In a third instance, its occupation will have commenced, 
and its festooned margin will be lined by the peripheral lamina of an Haversian 
system. Then, again, examples may be found where one side of a space is becoming 
the seat of a new system, while the opposite one is undergoing further enlargement. 
In no case is there any difficulty in distinguishing between an enlarging Haversian 
space and a developing Haversian system. The authors have preparations which 
show that these conditions of absorption and reproduction take place in old as well 
as in young or middle-aged subjects ; but it would appear that the frequency dimi- 
Q 2 
