Comparative%20Anatomy

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Comparative Anatomy

• Evolution of the Postcranial Skeleton

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Evolution of the Postcranial Skeleton.

• Functional units of the post-cranial skeleton.
• Visceal skeleton
• Vertebral column
• Ribs
• Sternum

• Girdles
• Paired appendages
• Unpaired appendages

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Postcranial Skeleton

• We need to know a little more about bone.
• What sorts of forces operate on bony tissue?
• Compression
• Tension
• Shear
• Torsion

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Forces operating on bone

• Examples
• Compression. Graviportal limbs of
  elephants.
• Shear..Greater trochanter of the femur.
• Torsion... Vertebrae Femur
• Tension.. Sternum

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Forces operating on bone

• Bone is living tissue, and accommodates whatever
  forces are applied to it.
• As an example, someone who loses a lot of weight
  quickly will still possess a robust skeleton
  designed to carry a lot of weight. However, with
  time the skeleton will reabsorb a considerable
  amount of tissue and become more gracile.

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Forces acting on bone.

• We can look at cross-sections of bone and
  determine exactly what kinds of forces were
  applied to the bone.
• Note - a bone is not solid in cross section.
• force lines within the bone become ossified for
  increased strength.

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Changes resulting from terrestrialization.

• What are some of the problems associated with a
  terrestrial life style?
• Support
• Stability
• Locomotion
• Respiration
• Dessication.
• Note some of these same issues are faced by
  aquatic forms as well.

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In an aquatic environment, the water acts as a
skeleton. Terrestrial organism often have their
mass arranged over only a few points of
support.Compare and contrast the articulations
of the 2 joints shown here.
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