28 CLASSIFICATION OF TISSUES. 
After bone has been decalcified what is the structure of the part 
remaining ? 
While the bone retains its original form, the lamella on being 
examined microscopically seem to be made up of an exceedingly fine 
network of decussating fibres, and to be perforated by minute holes. 
What are these holes supposed to form ? 
When the lamellee are placed together with these openings in apposi- 
tion it 1s supposed that they form canaliculi. 
What are Sharpey’s fibres ? 
If frum a decalcified flat bone you tease off a lamella, often there will 
be seen projecting from it small tapering fibres, which served to pin it to 
its adjacent lamella. They are never found in the concentric lamelle 
-of Haversian systems. 
What is periosteum ? 
It is a fibrous membrane which covers the external surfaces of bones. 
How many layers is it composed of ? 
Two—an outer and an inner layer. 
What is the structure of the outer layer? 
It is made up of white fibres, and contains numerous bloodvessels, 
lymphatic vessels and fine nerve fibres; occasionally fat-cells are found 
in this layer. 
What is the structure of the inner layer ? “0 REE? he 
It is composed of elastic tissue. m4 : ! 
What is the office of the periosteum ? 
To support vessels for the nutriment of bone. When it is destroyed 
the bone dies. , 
Where is marrow found ? 
In the medullary cavity of long bones, in the spaces in Spongy bone 
and in some Haversian canals. 
What are the varieties of marrow? 
From its color it may be divided into two varieties, yellow and red. 
Give the structure of yellow marrow. 
It is composed almost completely of fat-cells. 
What is the structure of red marrow ? 
Fat-cells, round cells resembling lymphoid cells, called marrow cells, 
and large granular cells having several nuclei, these last are called: 
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