To learn how the human body works in a first-handed and personal way, there are three primary sources of evidence that I think a teacher should rely upon heavily in an elementary classroom: one's own body, the dissection of animals that resemble human beings, and an atlas of human anatomy. (If you grow up to become a surgeon, you will dissect real human cadavers for practice, but in an elementary classroom, an atlas of anatomy, plus whatever x-rays and skeletons you can find to study, is the next best thing. In the modern world, there are also a few “plastination museums” that allow you to see the insides of real human bodies.) To study bones and skeletons, one can also visit museums, study real skeletons, and study x-rays...perhaps a student's own x-rays.
Atlases of Anatomy
I never liked cartoon pictures in science books. They are too unrealistic and oversimplified and you have no motivation to examine them or study them closely. For studying the human body, I much prefer showing students pictures from a real, actual atlas of human anatomy, prepared by professionals who have seen what human bodies look like inside for themselves, and who can draw them well to show the rest of us what they look like. These pictures allow you to analyze details, and to compare and contrast different features and different structures from different parts of the body. The students seem to like it, too. Most of them appreciate not being “talked down to”, and being able to study the same books that the adults use, rather than cartoons that bear little resemblance to reality.
Using an atlas of human anatomy in conjunction with the dissection of animals not only gives you a real sense of textures and appearances in real bodies, it also allows you to compare and contrast. You can discover the common patterns in all mammals and vertebrates, as well as curious and interesting differences between people and other animals. You can see the theme and the variations. A good atlas will also include pictures of “normal anatomic variants”, which help students realize that even among individual human beings, there are variations on the theme. People are similar on the inside, but not identical.
My favorite atlases of anatomy are the ones containing the wonderful drawings of Frank Netter. There's even a coloring book version, although I've never used that one personally.
Biology Supply Companies and Dissection Supplies
You don't have to purchase preserved specimens from a specialty supply company in order to dissect animals or their parts. Many muscles and bones are available at the meat counter of your supermarket, and you can often find internal organs to dissect as well. Ethnic markets in larger cities are a great source of offal for dissection. Fresh specimens are not only cheaper, they are often more realistic and more pleasant and easier to work with than preserved specimens.
For preserved biological specimens, I have purchased supplies from both Carolina Biological Supply Company, a major corporation, and the smaller discount company Bio Corporation. Of the two, I recommend Carolina hands down, unless you are on a very thin budget. Carolina's specimens are more consistent and are much “fresher” in the color and texture of the flesh. The specimens from the latter are uglier and more rubbery, and I have received a few fetal pigs from them which were filled inside with some kind of disgusting goop — a clotted soup of blood and preservative, if I had to guess — although not all of their pigs were this way. The preservative that Bio Corp uses for “dry” specimens is so pungent that it causes physical pain if the vapors get in your eyes or nose.
Nevertheless, the specimens from Bio Corporation can be worked with, and are definitely much cheaper than those from Carolina. Furthermore, you can get some pretty remarkable things from them that aren't available elsewhere. For example, one of the most fun demonstrations I performed one year involved a sheep's head, sawn down the midline to reveal a “medial sagittal section.”
So to summarize my experience with different companies: It might be a good idea to purchase specimens from a discount supplier like Bio Corp if you are on a tight budget, or if you are looking for certain specialized items, but otherwise stick to a major, reputable company like Carolina.
You will usually have a few options among specimens to choose from. Many preserved specimens can be purchased either “dry” or “wet.” I don't have any useful advice to offer here — it just depends on the nature of the specimen and on what you want to do with it. For example, if you want to dissect an eyeball, I recommend buying a pail of them, especially if you are buying them in bulk for a classroom. But for sheep pluck, I think the dry, vacuum-packed specimen is less sloppy and more convenient.
Another option that biology supply companies usually offer is color-injection. If you want, the company will inject one, two, or three colored dyes into the various tubular passageways of the body, helping you to distinguish between them. However, this is more expensive, and it damages the specimen a little, since they need to create an opening in which to inject the dye. In my experience, it also has limited usefulness. I generally prefer the cheaper and more natural “plain” versions, although you may have a different preference.
Many organs can also be obtained from your choice of animal. For studying human (i.e. mammalian) anatomy, I'd usually recommend sheep or pig parts, although for dissecting eyeballs, I'd recommend cow eyes over the others, since they are a bit larger.
For dissection equipment, you may be tempted to purchase a dissection kit, but it isn't necessary. In fact, I think the scissors in my dissection kits were essentially useless. They were uncomfortable to hold, and didn't have a strong shearing action, meaning they didn't cut well at all. I found that normal plastic-handled children's scissors from the kindergarten classroom worked much better. They were more comfortable, and did a better job cutting through tough material. Scalpels are very useful in many dissections, and you may want to order a few scalpel handles and blades, although you could also use hobby knives from a craft store. A blunt probe is also very useful to gently lift things and pry things one way or another, but you could use many substitutes: an old pencil or pen, or even kitchen utensils. For tougher organs, like hearts and kidneys, you may want to have a kitchen shears handy.
You may also want to purchase latex gloves from the drug store. Personally, I preferred to just work directly with my hands unless the specimens were of low quality, but my students almost always wanted gloves. The preservative does tend to make your hands a bit “pruny” and uncomfortable after extended contact. Dissection trays are useful in a classroom, but at home you could just as well use dinner plates or a baking tray.