Covering, Support, and Movement of the Body
sesamoid bones act to alter the direction of pull of a tendon.
Te function of others is not known.
Flat bones
are thin, flattened, and usually a bit curved. Te
sternum (breastbone), scapulae (shoulder blades), ribs, and
most skull bones are flat bones (Figure 6.2c).
Irregular bones
have complicated shapes that fit none of the
preceding classes. Examples include the vertebrae and the
hip bones (Figure 6.2b).
Check Your Understanding
What are the components of the axial skeleton?
Contrast the general function of the axial skeleton to that of
the appendicular skeleton.
What bone class do the ribs and skull bones fall into?
For answers, see Appendix H.
Functions of Bones
List and describe seven important functions of bones.
Our bones perform seven important functions:
Bones provide a framework that supports the body
and cradles its so± organs. For example, bones of lower limbs
act as pillars to support the body trunk when we stand, and
the rib cage supports the thoracic wall.
Te fused bones of the skull protect the brain.
Te vertebrae surround the spinal cord, and the rib cage
helps protect the vital organs of the thorax.
Skeletal muscles, which attach to bones by ten-
dons, use bones as levers to move the body and its parts. As a
result, we can walk, grasp objects, and breathe. Te design of
joints determines the types of movement possible.
(a) Long bone (humerus)
(b) Irregular bone (vertebra),
right lateral view
(d) Short bone (talus)
(c) Flat bone (sternum)
Figure 6.2
Classification of bones on the basis of shape.
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