MM. Debiene; "the feral reader"

Hello,

1.
What follows is a sentence quoted from the English translated version of The Phantom of the Opera.

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It was the evening on which MM. Debienne and Poligny, the managers of the Opera, were giving a last gala performance to mark their retirement.
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What is the MM. short for?
It seems to be a title, perhaps in French? (because the setting is in France.)

2.
What follows is a sentence quoted from the cover description of The Thirteenth Tale.

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The Thirteenth Tale is a love letter to reading, a book for the feral reader in all of us, a return to that rich vein of storytelling that our parents loved and that we loved as children.
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What does "the feral reader" mean here?
Does it mean the primitive desire for reading in humans' spirits?

Best Wishes