Dissection Lab
Report
APHY101
Athena Goulet
December 11, 2012
Investigative Question
How is the physiology of the sheep brain & cow
eye correlated to the anatomy seen during the
dissection of the two specimen?
Introduction
Why are the sheep brain and cow eye used
to study human anatomy?
These organs are similar to a human's organs
and therefore we can learn a lot about human
anatomy by studying the anatomy of animals,
particularly other mammals. They are also
easier to acquire and relatively inexpensive to
acquire compared to human organs.
Introduction, continued
What is the significance of the investigative
question?
We study anatomy because understanding
anatomy helps us understand physiology, or
how life functions. Understanding and labeling
complicated anatomical structures (anatomy)
would not be useful if the purposes of those
structures were unknown.
Hypothesis
What were your initial thoughts about the
about the answer to the investigative
question?
I was thinking about the possible differences
between a sheep eye and brain and a human's
and I imagined there was a great deal of
difference. I was also interested to see how
much detail and how many unique structures
could be discovered during the dissection.
Methods
What types of observations did you look at? I noticed that most of the tissue
was the same color and density in the brain. The eye seemed to consist of a
wide variety of tissue types, however.
How were the incisions performed?
Slowly, carefully, with constant pressure. I attempted to not cut any areas that
might get in the way.
What are some of the mini-experiments you conducted? I tested the
strength of the lens by pressing on it and found it to be surprisingly strong. I am
uncertain if that was from the natural structure of the lens or from the
preservation process. I was also interested in distinguishing the white matter
(myelinated neurons) from the gray matter (unmyelinated neurons.) I made a
coronal cut in to the frontal lobe and was able to distinguish the type types very
easily.
Results
Sheep Brain
Gross Examination
Results
Locate the protective covering of the brain – list the meninges in order.
Meninges (from outermost to innermost)
● dura mater
● arachnoid mater
● pia mater
Results
Locate the gyri of the brain, the sulci and the fissures – what are their
differences?
gyri - complex winding
structures, highest
ridges
● sulci - shallow grooves
that separate lobes
from each other
● fissures - very deep
grooves such as the
groove that separates
the left from right
hemispheres and the
cerebrum from the
cerebellum
●
Results
The blood vessels that were on the
brain were very small and difficult to
remove. Good effort was made to
remove them from the smaller
structures on the ventral side.
Blood vessels are between the arachnoid layer and the pia mater – you will
want to remove these vessels and the arachnoid layer if they are still present
on your brain. This is done by “gross dissection” – in other words – you do not
cut, you pull them away gently with the forceps.
Results
Locate the Brainstem
which consists of the:
●
●
●
Pons
Medulla
Cerebellum
Results
pituitary
gland
Find the Pituitary Gland if still present – if it has been removed see if you can
locate its root.
Results
olfactory bulbs (appear
to have been cut off)
Examine more closely the ventral side of the brain.
You should be able to see the Olfactory Bulbs – one under each lobe of the
frontal cortex.
Results
optic nerve
optic chiasm
Locate and examine the Optic nerve which protrudes from the ventral side of
the brain.
Can you see where the nerves from the right and left eye meet in the center to
form the Optic Chiasm?
Results
Locate now the 4 lobes of the Cerebrum:
parietal
occipital
temporal
frontal
Results
Sheep Brain
Dissection
Results
Make a midsagittal cut by holding the brain level and flat – cut along the
longitudinal fissure.
You should be able to locate the ventricles of the brain.
Results
Try to locate the Lateral Ventricles, the Septum, the Third Ventricle and the
Cerebral Aqueduct.
lateral ventricles
septum pellucidum
third ventricle
cerebral
aquaduct
Results
pineal gland
Try to locate the following structures:
Corpus Callosum – Genu, Splenium,
and the body of Corpus Callosum
massa intermedia or
interthalamic adhesion
Hypothalamus
Results
cerebellum
Locate the Cerebellum. Notice it resembles a tree like structure.
Results
Basal Ganglia
Locate the Basal Ganglia: Putamen, Globus Pallidus, and Caudate Nucleus
Results
Unable to locate the
trapezoid body and
decussating fibers
deep in the brain
fourth ventricle
Cut into the Cerebellum and the Brain stem. See if you can locate the Trapezoid Body and the Decussating Fibers – how
about the fourth ventricle? It should be seen clearly now.
Results
Sheep Eye
Gross Examination
and Dissection
Results
cornea
adipose tissue
sclera
optic nerve
remnant of an extrinsic eye muscle
Examine the external surface of the eye, noticing the thick cushion of adipose tissue.
Identify the optic nerve as it leaves the eyeball, the cut remnants of the extrinsic eye muscles, the conjunctiva, the sclera,
and the cornea.
The normally transparent cornea is opalescent or opaque if the eye has been preserved.
Results
conjunctiva
Examine the external surface of the eye, noticing the thick cushion of adipose tissue.
Identify the optic nerve as it leaves the eyeball, the cut remnants of the extrinsic eye muscles, the conjunctiva, the sclera,
and the cornea.
The normally transparent cornea is opalescent or opaque if the eye has been preserved.
Results
Trim away most of the fat and connective tissue but leave the optic nerve intact. Holding the eye with the cornea facing
downward, carefully make an incision with a sharp scalpel into the sclera, about ¼ inch above the cornea. The sclera of the
preserved eyeball is very tough so you will have to apply substantial pressure to penetrate it. But work gingerly because
some of the fluid may squirt out of the eyeball when the sclera is pierced. Then, using scissors, cut around the circumference
of the eyeball, paralleling the corneal edge.
Results
choroid and tapetum lucidum
cornea
vitreous body
posterior part
anterior part
Carefully lift the anterior part of the eyeball away from the posterior portion. Conditions being proper, the vitreous body should
remain with the posterior part of the eyeball. Move some of the vitreous humor aside to view the pigmented choroid coat and
tapetum lucidum.
Results
lens ciliary zonule
lens
anterior of cornea
removing the lens
iris
ciliary body
Examine the anterior part of the eye and identify the ciliary body, lens ciliary zonule, iris and cornea.
Results
vitreous humor
(clear sac)
retina (appears to have
come off with the vitreous
humor and it was attached
at the optic disk to the
posterior of the eye
Examine the posterior portion of the eyeball.
Remove the vitreous humor, and identify the retina.
Discussion
Was your hypothesis correct? Why or why not? The
two organs were more similar to human organs than I
thought so my hypothesis that the organs would be very
different was incorrect. However, there were some small
differences. The sheep had a differently shaped iris, but the
lens was the same shape behind it. And the shape of the
brain seemed more football-shaped than that of a human's
with a more prominent brainstem and cerebellum.
Discussion, continued
What were some of the evidences you found in your
autopsy that answered the investigative question? The
back of the eye had an additional structure that the human
eye lacks called the tapetum lucidum and it was very
prominent. The cerebellum also appeared to be much
larger than a human's would be. However, for the most
part, I could identify many of the areas of each organ from
my studies of the human body.
Discussion, continued
What are further questions for investigation
that you still have? As I mentioned previously,
the hardness of the lens interested me. The
lens changes shape to focus on different visual
targets, and I imagined it would be more
flexible. The ventricles also seemed quite close
together. Again, I wonder if this was from the
preservation process, or if the ventricles are
more prominent when the animal is alive.
The End