What is the etymological reason for words like 胸, 肘, 腹, 腕, and 脚 to have 月?

Is it phonetic at all or does it contribute meaning?
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2019-05-30T18:12:49.177
68589
2019-05-30T18:12:49.177
33900
question
kanji etymology
Why do so many kanji for body parts have the radical 「月」？