The Adam’s apple is actually a protruding piece of thyroid cartilage that develops at puberty, but only in the male. It is so-called because it is said to symbolize the piece of the apple of knowledge that got stuck in Adam’s throat after Eve, encouraged by the serpent, coaxed him into eating the fruit.
The Adam’s apple can be a bit of a pain in the neck for transsexuals, cross-dressers, and female impersonators, since it can be the one giveaway sign that the apparently well-dressed lady is in fact a gentleman. The offending lump can, however, be removed by surgery.
From: The Element Encyclopedia of Secret Signs and Symbols