We refer to these as such:
It's the antlers that we're concerned with. Antlers, or horns in sheep and cattle, are a giveaway that the animal is a mature male. Meanwhile, we also refer to this with the same term:
Yes, we're talking about boobs. Again, they're a sure biological sign that we're looking at (and quite distractedly, I must add) a mature woman. So somehow, we took the term the term for the second most distinctive male physical characteristic in the animal kingdom and used it as a slang term for the second most distinctive indication of human femininity.
Is this a current thing? Is the meaning of rack as slang-for-breasts a recent development, or does it have more of a history than I would guess? The internet doesn't have a clear answer so for the time being I'm at a loss.
This confuses me, if I think too much:
Uh... nice rack(s)?