There's no better way to really understand human anatomy than to build it from the bones on up. It's a lot easier than you might think. It's also a lot more informative and skill building. Once you build a perfect skeleton, then lay on the musculature and finally the skin, you'll be miles ahead of where you were at when you started.
Here's the early stages of Jack Skellington.
It can take a while to get the proportions correct, but once you get them you'll never be non-plussed when facing a model.
Here's an example of the skull with the musculature laid on top. Some sections of skin were laid in with different colored clays to give a more lifelike effect.
The blue indicates the aponeurosis (after doing a few of these you'll be able to toss around terms like epicranial aponeurosis, nuchal lines and occipital protuberance with the best of them). You can get these colored clays at the crafts store and use a hair dryer to warm them and make them smooth. Lots of fun...and a good learning experience.
Here a version done with the musculature and skin indicated as a single surface (but we know what's going on underneath, don't we).
You certainly will know what's happening under the skin once your begin making ecorche studies. The clay is the oil-based Plastilene, not the stuff that can be fired. Plastilene and microcrystalline wax offer many different finishing effects you simply cannot get with traditional clay. That's why the model-makers for movies and cars use it.