Mammalian Brain Anatomy-The Sheep Brain
Background
Mammalian brains have many features in common and since human brains are not readily available, sheep
brains are often dissected as an aid to understanding mammalian brain structure. However, the adaptations
and ecology of these animals differ from those of the humans, so that comparisons of their structural features
may not be precise.
Focus Questions
What are the major anatomical features of sheep brains and their functions?
What are the important similarities and difference between sheep and human brains?
Procedure
Your group will put together a formal lab write up for the Sheep Brain dissection. You will submit a hard copy
of the lab which will need to be typed up with actual photos inserted, drawings attached and formal written
conclusions. Before you begin observing, have your scribe write a title, purpose and hypothesis for the lab on
the handout give. Your hypothesis should predict what differences you would expect to see in the sheep brain
as compared to the human brain and your group’s reasoning. Discuss this and write your answers.
A. External Anatomy- Record your data in the table provided.
1. Obtain a preserved sheep brain. Rinse it thoroughly in water to remove the preserving fluid. Wear
gloves when you handle the sheep brain.
2. Conduct a series of quantitative measurements on your sheep brain. Find the following: volume of the
brain (mL), the total length(mm), the total width (mm). You should also measure any three (3) additional
dimensions or structures that you feel are significant.
3. Write down 5 physical characteristics/observations of the external anatomy. Be detailed in your
description of each characteristic.
4. Examine the surface of the brain for the presence of the meninges. If they are present, located the
following: dura mater-the thick opaque outer layer: arachnoid mater-the delicate, transparent middle
layer which is attached to the under surface of the dura mater; pia mater-the thin, vascular layer that
adheres to the surface of the brain. Remove any remaining dura mater by pulling it gently from the
surface of the brain.
5. Position the brain with its ventral surface down in the dissecting tray. Carefully observe the brain,
comparing it with the available diagrams. Make an accurate scaled drawing of the ventral surface
down. Label the following structures: cerebral hemispheres; gyryus/sulci, longitudinal fissure; frontal
lobe; parietal lobe; temporal lobe; occipital lobe; cerebellum and medulla oblongata.
6. Gently separate the cerebral hemispheres with your fingers (do not separate, cut or break apart the
hemispheres) along the longitudinal fissure. Identify the corpus callosum, which appears as the
transverse band of white fibers within the fissure that connects the hemispheres.
7. Bend the cerebellum and medulla oblongata slightly downward and away from the cerebrum. Identify
the pineal gland in the upper midline.
8. Position the brain with its ventral surface upward. Carefully observe the brain, comparing it with the
available diagrams. Make an accurate and scaled drawing of the ventral surface up. Label the
following structures: longitudinal fissure; olfactory bulbs; optic nerve, optic chiasma; optic tract; pituitary
gland (may be missing) and the pons.
9. Although some of the cranial nerves may be missing, small and difficult to find, use available diagrams
to locate as many as possible. Label as many of the following as possible: occulomotor nerve,
trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve,
glossopharyngeal nerve, vagus nerve, accessory nerve and hypoglossal nerve.
B. Internal Anatomy
10. Using a long, sharp knife, cut the brain along the midline to produce a median (or midsagittal) section.
Carefully observe the brain, comparing it with the available diagrams. Make an accurate, scaled
drawing of the internal anatomy for part B. Label the following structures: cerebral cortex; white
matter; gray matter; olfactory bulb; corpus callosum; brain stem; optic chiasma; pituitary gland;
thalamus; hypothalamus; pineal gland; pons; and medulla oblongata.
11. Dispose of your sheep brain as directed. Clean and dry your dissecting equipment and show your
teacher your materials to be checked off.
C. Anatomical Comparisons and observations
12. Compare your sheep brain with available diagrams of the human brain. Note any important
comparisons in this section. (part C)
D. Analysis and conclusion
1. Complete a table like the one provided on your own paper
Structure
Cerebral cortex
Longitudinal fissure
Cerebellum
Medulla oblongata
Olfactory bulb
Optic chiasma
Optic tract
Pituitary gland
Pons
White mater
Gray matter
Corpus callosum
Thalamus
Hypothalamus
Pineal gland
Amygdala
Occulomotor nerve
Trigeminal nerve
Vagus nerve
Function
2. Identify the structures of the brain involved in the following actions:
a. You sing along with the lyrics to a favorite song.
b. You take a big sip of milk that is spoiled and it makes you vomit.
c. You are a soccer goalie who makes a diving save of a penalty kick.
d. You are a physiology student who finally understands brain anatomy after reading the textbook.
3. Write a brief comparison of the brain you dissected and the human brain. Are there any evolutionary
relationships for the anatomical differences you have noted?
4. Write a conclusion to the lab and explain what you have gained from this dissection. Were your
predictions correct? Explain.
Brain Dissection Lab Data
Purpose:
Hypothesis:
Part A: External Anatomy
Measurements:
Volume
Total length
Total Width
(ml)
(mm)
(mm)
Group Choice
Group Choice
Observations:
1.
2.
3.
4.
5.
Drawing: Ventral Surface Down
Title:
Scale:
Group Choice
Drawing: Ventral Surface Up
Title:
Scale:
Part B: Internal Anatomy
Drawing: Median Section
Title:
Part C:
Scale: