One can safely assume that a voluptuous woman with large breasts, even when wearing a dress with a modest neckline, would reveal some cleavage. Thin girls or women with small bosoms would not have as much difficulty following the rules of decorum. Before the 20th century, the feminine ideal was a woman whose curves were bounteous and whose figures were pleasingly plumb. Rich husbands and fathers were proud to show off their well-fed women. Only the poor, who toiled all day and never had enough to eat, or the sick, or those who were metabolically overchallenged, were thin and scrawny. Thus, it made sense that during the Regency heaving bosoms were de rigueur. But were they?
“The heaving Regency bosom, or was it? Some facts laid bare.” from Jane Austen’s World
A bit more on fashion and Pride and Prejudice. *boobs* ~S