Richard Mellish above found at least 2 other examples in Golden Vanity of the locution which, as I say above, I always use, "Bent to his breast". It seems to me an obvious ellipsis for "bent down as part of the process of lying on his breast in a swimming position in the water"; an alternative to diving in head first. That seems to make perfect sense to me.

Also, thanks Richard for answering my question-to-self as to where I got that 'to' from which does not seem to occur in many versions: probably from a version of Golden Vanity I heard or came across some time.

~M~