Anatomy reaches Late Latin anatomia and Greek anatomē, dissection. Behind that noun is anatemnein, formed from ana- and temnein: cutting up.
The literal phrase explains the historical formation. Modern anatomy is broader than the act of dissection, and ana- has other meanings in other formations.
Sources
- Merriam-Webster: anatomy
Word History supplies the dissection route and component verb; the definitions distinguish structure, study and dissection.
- Merriam-Webster: ana-
The prefix section gives up and traces it to Greek ana.
- Online Etymology Dictionary: atom
Atom: Greek *atomos* “uncut”, from a- “not” + *tomos* “a cutting”, from *temnein* “to cut”