Rat Dissection

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Rat Dissection
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ts/rha/lowres/rhan786l.jpg
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Daily grade rubric for group All members are
responsible for meeting these criteria. If I, the
fair and impartial judge, determine you are
responsible for bringing your group down, you may
find yourself doing seatwork, not dissecting.
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The Anatomy of the Rat
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Instruments

• 1.Probe can be used to lift structures, move
  aside.
• 2.Forceps, to grab and move, not as gentle
  perhaps as probe.
• 3.Scalpel to make clean cuts, always cut away
  from you, keeping fingers well below the blade.

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More stuff

• Scissors
• Pins, hold specimen in place.
• Pan with pad on which the specimen rests.
• Gloves
• Apron, goggles, zip lock bag

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The Classification of the Rat

• Kingdom AnimaliaPhylum ChordataSubphylum
  VertebrataClass MammaliaOrder RodentiaFamily
  MuridaeGenus RattusSpecies norvegicus

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Anatomical Areas

• Anterior
• Posterior
• Dorsal
• Ventral

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Terms
Definitions from free dictionary.com

• Dissection
• To examine, analyze, or criticize in minute
  detail
• Anterior
• Located on or near the front of the body in
  higher animals.
• Posterior
• Relating to the caudal end of the body in
  quadrupeds or the dorsal side in humans and other
  primates
• Dorsal
• Of, toward, on, in, or near the back or upper
  surface of an organ, part, or organism.
• Ventral
• Relating to or situated on or close to the
  anterior aspect of the human body or the lower
  surface of the body of an animal.

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Getting started

• You may have one pair of gloves. Check they have
  no holes.
• One member of your group obtain a rat.
• Run it under water for several seconds, pat dry.
  Place in a pan.
• Another member should pick up your group number
  scalpel, 1-2 scissors, 2-3 probes, and several
  pins.

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External observations

• What observable characteristics does your rat
  have consistent with Class Mammalia?
•  
• Compare/contrast your specimen with at least two
  others. Note at least 3 observable variations
  within species.
• Is your rat male or female? _______ How do you
  know?

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External observations

• 1. Note the hairy coat that covers the rat and
  the sensory hairs, whiskers.
• 2. The mouth has a large cleft in the upper lip
  which exposes large front incisors that continue
  to grow for as long as the rat lives. What might
  be adaptive about that? Under what circumstances
  could you imagine, that would become less
  adaptive?
• 3. Note the eyes with the large pupil and the
  nictitating membrane found at the inside corner
  of the eye. This membrane can be drawn across the
  eye for protection.
• 4. Are there external ears? What is adaptive
  about that? Would it be advantageous for an
  aquatic animal to have them? Explain.

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External observations

• 5. Locate the teats on the ventral surface of the
  rat. Check a rat of another sex and determine
  whether both sexes have teats.
• 6. Examine the tail, the tails of rats do not
  have hair. Can you think of any adaptive reason
  for that?
• 7. Locate the anus, which is ventral to the base
  of the tale.
• 8. On female rats, just posterior to the last
  pair of teats, you will find the urinary aperture
  and behind that the vaginal orifice which is in a
  small depression called the vulva. 9. On males,
  you will find a large pair of of scrotal sacs
  which contain testes. Just anterior to the
  scrotal sacs is the prepuce, which is a bulge of
  skin surrounding the penis. The end of the penis
  has a urogenital orifice, where both urine and
  sperm exit.

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Variation within species

• Contrast 3 specific structures of your specimen
  with at least two other specimens.

animal.discovery.com/.../smartrat_zoom.jpg
www.popsci.com/.../files/articles/rat2.jpg
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Skinning

• Use your scissors to cut through the dermis only
  according to the diagram.

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Motions of Muscles

• Extend
• Lengthen

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The Thoracic Organs

• Cut through the abdominal wall of the rat Be
  careful not to cut too deeply and keep the tip of
  your scissors pointed upwards. Do not damage the
  underlying structures!
• 1. Locate the diaphragm, which is a thin layer of
  muscle that separates the thoracic cavity from
  the abdominal cavity.
• 2. The heart is centrally located in the thoracic
  cavity. The two dark colored chambers at the top
  are the atria (single atrium), and the bottom
  chambers are the ventricles. The heart is covered
  by a thin membrane called the pericardium.

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Thoracic organs

• 3. Locate the thymus gland, which lies directly
  over the upper part of the heart. The thymus
  functions in the development of the immune system
  and is much larger in young rats than it is in
  older rats. Is your rat old or young? How do you
  know?
• 4. The bronchial tubes branch from the trachea
  and enter the lungs on either side. The lungs are
  large spongy tissue that take up a large amount
  of the thoracic cavity. Bronchial tubes may be
  difficult to locate because they are embedded in
  the lungs.