the bones may rise the bones may sink..

"The bones may rise the bones may sink, but the meat stays sunk." I'm not getting that. When I meditate and I'm breathing in & out, there are two ways that I know to breathe. One is abdominal breathing where the stomach goes in and out, the other is diaphragmatic breathing where the stomach does not go in and out as the attention is more on the diaphragm but the chest tends to rise and fall a little. Should I be doing one of these types of breathing, something else altogether or is it unimportant? What bones are supposed to be rising? What meat is supposed to be sinking? All the bones and all the meat or are we talking about the torso specifically? I'm completely lost on this concept. All I feel is my stomach moving in and out or my diaphragm & chest moving up and down...