CONNECTIVE TISSUES. 27 
Where is compact bone found ? 
In the walls of the long bones, and in the outer and inner plates of 
flat bones. 
Where is cancellous bone found ? 
In the heads of the long bones and between the plates of the flat 
bones. 
Upon what does the difference between these two classes of bone 
depend ? 
It depends upon the difference in the amount of earthy matter. In 
compact bone the earthy matter is abundanc and the spaces small; in 
cancellous bone the earthy matter is scant in amount and the spaces 
are large. 
What are the spaces in compact bone called? 
Haversian canals. 
What is the structure of compact bone? 
It is made up of an intercellular substance; in this basement sub- 
stance are little spaces containing delicate branching cells. The inter- 
cellular or basement substance is impregnated with salts of lime, which 
gives the bone its hardness. 
What are these spaces called ? 
Lacune. 
What are canaliculi ? 
They are small delicate canals connecting lacunze one with another, 
and also with the Haversian canals. 
What is an Haversian system? 
When an Haversian canal is cut transversely, the hard substance of 
bone will be seen arranged around it in concentric rings or lamelle. 
Between these lamell will be seen little spaces or lacunze connected by 
canaliculi. Each lacuna contains a delicate branching cell called a bone- 
cell. The whole taken together is an Haversian system. 
How is the shaft of a long bone made up ? 
Of multitudes of these Haversian systems, the spaces between which 
are filled by irregularly arranged lamellz of bone. 
What is the structure of cancellous bone? 
This is composed of thin plates and interlacing spiculz of bone, 
which in turn are made up of several lamellz of bone superimposed 
one upon the other in several layers. 
