Dissecting Organs from the Deli
Fresh offal can provide cheap specimens of internal organs for exploration.
Nearly every part of a mammalian body is edible.
Some parts are tough and not pleasant to chew, but
still can be eaten and contain nutritional value. Beef
stomachs are available as "tripe", intestines are
often used as sausage casings, brains are a
delicacy in some countries, and even bones can be
boiled to make broth, or ground up into "bone meal",
which was once used as a dietary supplement and
in animal feed. Only teeth, fur, and claws are
useless as food.
The most tender and popular parts are usually the
muscles or meat, and this is readily available. The
larger internal organs are not as popular in
American cuisine, but I can find sliced calf liver in
most supermarkets, and whole organs of several
kinds can often be found at ethnic or specialty meat
markets. (Internal organs sold as food are
called offal.) I have little problem finding livers,
hearts, kidneys, and tongues of sheep and cows.
The only exceptions are brains and lungs. For some
reason, lungs are illegal to sell as food in the U.S.,
although they are popular in the cuisine of some
other countries. As nearly as I can tell, brains are
legal as food in the U.S., but are not often sold,
either due to the risks of brain-borne diseases, or
simply to the difficulty in extracting them from the
cranium. I found frozen cow brains once in a
specialty meat market, and now I really wish I had
bought one, because I have never found them since.
The availability of fresh offal provides the home
anatomist with opportunities for dissection and firsthand observation of the structure of organs.
Besides being cheap, these organs also have the
advantage that they are much fresher, more
realistic, and easier to work with than preserved
specimens purchased from a biology supply
company. I purchased all of the following sheep
organs from a nearby Middle Eastern deli for
roughly two dollars apiece. (Most organs available
from sheep are also available from cows, but these
are often too large to be convenient for dissecting.) I
purchased the chicken organs and beef tripe from
my corner grocery store. For the most part, kitchen
knives and kitchen shears work fine for dissecting
these organs. However, you may find a scalpel (or
hobby knife) to be helpful—much of the fabric in the
kidney and heart is very tough and difficult to cut
with a kitchen knife.
Lamb Kidney
A kidney is a bean-shaped organ with one
"doorway" on the concave side through which all of
the tubes come and go. This doorway into the
kidney is named the hilum. (Lungs also have hila.)
Notice that there are three tubes running through
the doorway—the ureter, which connects the kidney
to the bladder, and two blood vessels, which
connect the kidney to the two major blood vessels
alongside the spine: the renal artery, which
connects to the aorta, and the renal vein, which
connects to the vena cava. A clue to distinguishing
between the renal artery and the renal vein is that
arteries have muscular walls, and so are thicker and
more elastic than veins.
A Lamb's Kidney
If you slice through a kidney along the midplane,
you discover a complex interwoven structure inside.
The three tube systems branch out and blend
together in the spongy material around the edges of
the organ—the cortex of the kidney. Between the
hilum and the cortex, the tube systems pass back
and forth through various branches and the
distinctive renal pyramids.
The Interior of a Lamb's Kidney (click to enlarge)
I tried putting the two halves back together and
cutting through the kidney sideways, or transversely.
The result is more or less what you would expect:
Inside A Lamb's Kidney
Lamb Heart
The heart is an oblong muscular organ, which is
attached to the lungs and to the two major blood
vessels of the body (the aorta and vena cava again)
by a tangle of tubes at the top. There are also two
"flaps" lying alongside the tube tangle which bear a
vague resemblance to the external flaps of human
ears, and which share their name: auricles. The
probe in the following two pictures indicates the
auricles. At the other end from tube tangle, the
heart tapers to a muscular peak, called the apex of
the heart. It is the bumping of this apex against the
inside of your sternum that you feel as a heartbeat
in your chest.
A Lamb's Heart
The Tube Tangle
If you wish to slice through a heart to expose the
interior, which way should you slice? If the auricles
indicate the "sides" of the heart, then a good choice
for which way to slice is sideways, through each
auricle, so you can see what is inside underneath
each auricle. In the heart shown below, I sliced
through one auricle, but missed the other. The
second auricle is hidden behind the top of the right
ventricle in the photo below.
The Interior of a Lamb's Heart (click to enlarge)
The heart is hollow inside, with two chambers, one
underneath each auricle. These are the ventricles.
The larger of the two, with thicker more powerful
walls, is normally on the left side of the body and is
called the left ventricle, and the smaller of the two,
with thinner walls, is the right ventricle. (If the heart
is made to work by the muscular walls, which of the
two chambers do you suppose has the harder job to
do?) Within and underneath the auricles are two
floppy chambers that look like either the upper
portion of the ventricles, or maybe separate
chambers atop each ventricle. These are the atria.
(The right atrium is hidden in the picture above.) A
little poking and lifting with a blunt probe (or an old
pencil or pen) can reveal tough thin fabric flaps
separating the ventricles from the atria. (When
these flaps are lying flat against the walls, each
atria and ventricle looks like a single chamber.) The
visible tendon-like strings apparently hold down the
edges of the flap for some reason. If you gently
insert the probe through the various tubes in the top
of the heart, it will emerge within one of the
chambers. All of the tubes on top of the heart open
into one of the chambers within.
(The flaps between the atria and ventricles are
the mitral valve and the tricuspid valve—one-way
valves that let blood flow from the atria to the
ventricles, but not vice versa. The tendons—
the chordae tendinae, or heart strings—are for
holding the valve steady when it is closed so that it
doesn't blow inside out like an umbrella in the wind.
The little lumpy muscles lining the interior walls that
pull on these tendons are the papillary muscles.)
Chicken Hearts
I bought a package of chicken hearts and gizzards
from my corner grocery store for about three dollars.
On the whole, I don't recommend dissecting
chicken hearts, due to their small size. They may be
interesting as a comparative study, however,
especially if you or your students enjoy meticulous
work with a magnifying lens.
Chicken Hearts
Livers
Most supermarkets sell sliced beef or calf liver, and
I can sometimes find chicken livers in my local
grocery store, or whole beef or lamb liver in my
nearby Middle Eastern market. However, liver tends
to disintegrate with excessive handling, and I
haven't found much to observe about supermarket
liver anatomically, other than that they are
shapeless tattered sponges, with some tubes
running through them. (This is one case where
preserved specimens might be better than fresh.
The preservative tends to make the fabric rubbery,
so it holds its shape better.) Sometimes you can
find a portion of a branching system of large veins,
presumably the hepatic portal vein, or one of the
larger branches of it. (I've managed to find a way of
cooking sliced liver that makes a dish I actually
enjoy eating...except for those veins. Those large
veins just won't tenderize.)
Lamb Tongue
I purchased this lamb tongue from my local Middle
Eastern market for about two dollars, and cut it in
half with a kitchen shears. Notice the structure—the
bulk of the tongue is muscle, with a coating of skin.
It is hard to identify any more detail than this. I am
fairly certain I found a lingual nerve emerging from
the base of the tongue, but it can be hard to tell the
difference between nerves and connective fabric.
A Lamb's Tongue
The lingual papillae at the base of the tongue are
large and obvious to the unaided eye. The papillae
midway down the tongue are smaller, but can easily
be seen with the aid of a magnifying lens or lowpower dissecting microscope. The following picture
is a view of the papillae on the skin from the upper
surface of a lamb's tongue, midway between root
and tip, seen through a microscope.
The Surface of a Lamb's Tongue
Beef Stomach
I bought "beef tripe", which means beef stomach,
from my grocery store for a few dollars. It consists
of a tough leathery fabric — mostly the muscular
stomach wall — covered on the inside by various
ripples and folds. (The inner texture will be different
depending on which of the cow's several stomachs
the tripe comes from.) These folds correspond to
the gastric rugae in a human stomach.
Beef Tripe