434 
MOVEMENT 
while the adult wrist has well-formed bones. The transition 
from soft cartilage to hard bone is due to the formation of 
mineral matter that takes the place of the cartilage. 
The erect position of man gives to his skeleton important 
characteristics which the skeletons of other animals do 
not possess. Among these may be mentioned the curves 
Figure 383 . — X-ray of 
Hand of Child. 
The bones in the wrist 
are forming. Between the 
joints of the fingers are 
seen small bones that later 
unite with the bones of the 
hand. Compare with Fig¬ 
ure 384. 
Figure 384 . — X-ray of Hand 
of Adult. 
What changes have taken place 
since childhood ? 
in the spinal column, the large hip bones, and the heel and 
arch of the foot. 
342. Joints. — The numerous bones in the skeleton allow 
the body to move although giving a certain amount of rigidity 
and permanence of shape. Wherever two bones meet and 
allow movement, the term joint or, more technically, articula¬ 
tion, is applicable. The joints are divided into three classes : 
(1) Immovable joints (sutures), found in the skull of the 
