THE SKELETON 
433 
Figure 381 . — Cartilage. 
Note that the living cells are separated 
by spaces represented by small dots. 
more delicate organs of the 
body are protected further 
— the heart and lungs by 
the ribs, and the brain by 
the cranium. The skeleton 
and muscles of man are 
similar to the correspond¬ 
ing parts in the frog and 
the dog. Certain technical 
differences are noted by 
anatomists, but in general 
plan or structure and in 
their functions, the skeleton 
and muscles are alike in all 
the higher animals. 
341. The Skeleton. — Unlike the rest of the body the 
skeleton proper is hard. It consists of bone and a compara¬ 
tively soft substance known as carti¬ 
lage, or gristle. There are cells in 
the bones just as there are cells in 
the liver, the muscles, and in the 
nervous system. So, like the other 
parts of the body, the bones grow 
because the individual cells are sup¬ 
plied with food from the blood. 
Cartilage occurs near the ends of 
the bones, in the ear, and in the nose. 
It is especially prominent in the wrists 
and ankles of children. Therefore 
children should not be lifted by their 
hands or allowed to stand until a 
certain amount of bone has taken the 
place of this soft cartilage. This is 
readily appreciated when one examines an X-ray of the wrist 
of a child, which is almost entirely composed of soft cartilage 
Figure 382 . — Diagram to 
Show the Structure of 
Bone. 
The large circle, H, is a 
branch of the Haversian 
canal where the blood ves¬ 
sels are found. The spaces 
between the lines and oval 
black masses is bone. 
