Dissecting the Rat
Introduction to Mammals
 Of all the classes of animal life, mammals are
considered to be the most advanced.
 Examples: dogs, cats, squirrels, pigs, whales,
horses, sheep, and HUMANS!
 Vary greatly in size…from 2 inches (the shrew)
to 100 feet long (the blue whale)
Mammalian Characteristics
 Vertebrates (have backbones)
 Presence of lungs (breathe air)
 Warm-blooded (endothermic)
 This means that the body
temperature of a mammal stays
the same, no matter what the
outside temperature is
 4 chambered heart
Mammalian Characteristics, cont’d
 Give birth to live young


Monotremes – mammals that
lay eggs
EX: the platypus and the
echidna (spiny anteater)
Platypus
 Body Hair
 Produce milk (have mammary
glands)
Echidna
Mammalian Characteristics, con’t
 Less Obvious Characteristics
 The diaphragm separates the
heart and lungs from the
stomach
 Lower jaw has one bone on
each side
 Different types of teeth adapted
to different uses (tearing,
chewing)
 Brains are much more highly
developed than any other
animal
Comparative Anatomy
 Study of similarities and differences in the
anatomy (structure) of organisms
 Many aspects of structure and function are
identical between different species of mammals

Homologous Structures – same structure
(embryologically speaking), different function
(have a common evolutionary descent)


EX: wings of bats and arms of humans
Analogous Structures – different structure, same
function (evolved in a similar environment)

EX: wings of bats and wings of insects
Advantages to Dissection
 Dissection is a hands-on, investigatory kind of activity
for students. Dissection allows students to "test the
truthfulness" of what they see in books.
 Dissection impresses on students the normal variation
that is present in the natural world. No two rats, even
though they are perfectly normal, will look exactly the
same.
 In fact, to do well on practicals, students MUST looks at
several examples of each structure in different animals.
Occasionally, quite significant anatomical variations
(anomalies) will be noticed.
Safety and Handling
 Sharps
 All Dissecting tools should be
considered dangerous.
 Notify your teacher IMMEDIATELY
if you are cut.
 Handle probes, dissection scissors,
razor blades, etc. with extreme
caution.
 Always cut away from you, never
toward yourself or another person.
 Dissection specimens should be
properly mounted in the dissection
pan before cutting.
Safety and Handling, cont’d
 Do not place your hands near your mouth or eyes while
handling preserved specimens. Most of the preservatives
in use today are non-toxic to the skin, but they may
cause minor skin irritations. If the preservative gets on
your skin, wash with soap and warm water.
 If the preservative gets in your eyes, rinse them
thoroughly with the safety eyewash.
 Wear lab gloves and goggles at all times!
 Lab gloves and paper towels go in
the regular trash. Skin and pieces
of rat go into the separate plastic
bag at the front of the room
(NOT down the sink).
IMPORTANT!
 Do NOT rinse off your rat in the sink as you will wash
off the chemicals that keep it preserved!
 What do you think would happen as a result, if you did
rinse off your rat?
Dissection Helpful Points
 Actual cutting should be kept to a
MINIMUM
 Tissue are picked and teased apart with
needle probes, forceps, and blunt probes
in order to trace the pathways of blood
vessels, nerves, muscles, and other
structures.
 NEVER CUT OR MOVE MORE THAN
IS NECESSARY TO EXPOSE A GIVEN
PART.
 Compare dissections with other
students, especially students whose rat is
of a different sex. You will be
responsible for both sexes on the lab
practical (test).
Dissection Basics
 superior: above
 inferior: below
 anterior: toward the front of the body
 posterior: toward the back of the body
 medial: toward the midline
 lateral: away from the midline
 cranial: toward the head
 caudal: toward the tail
 dorsal: toward the back of the body
 ventral: toward the underside of the body
 proximal: nearer to the attachment site
 distal: farther from the attachment site
Dissection Basics, cont’d.
Dissection Basics, cont’d.
Identify the Regions of the Body
 Cranial Region: head
 Cervical Region: neck
 Thoracic Region: chest
 Abdominal region: front of the body; below
chest
 Femoral Region: thigh
Act Responsible!
 It is your responsibility to respect your rat.
 It had life and how has the purpose of teaching
you mammalian anatomy
 If you choose to disrespect the rat(if you have
to ask, then it is probably disrespect), you also
choose to be written up and be punished by the
principal…