Your first class may not teach this, but you'd get to it eventually if you kept taking classes. (Then again, your first class may at least mention this sort of thing at some point.) What the "average human" is is not what all humans are. There's all sorts of things like, the stuff in that link, major nerve clusters having additional or missing separations, extra separated or fused bones, major veins and arteries not being quite in the usual location... look close enough and you'll find something on everybody that doesn't match the "standard human anatomy".
