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 first-hand 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.
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.
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.
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:
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.
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 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.)
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.
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.)
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.
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 low-power 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.
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.