Question : what does "drawing out the bones" mean?

"drawing out the bones" is part of the technique to get the ch'i. It literally means that you extend through the body in such a way that the bones are separated.

To achieve this there is a feeling of extending outwards from the centre of the body in all directions. First the body must be 'rooted.' This means that the weight is allowed to sink after body alignment and deep relaxation. The downward sensation accumulates in the lower body centred around the lower tan tien (roughly three finger widths below the navel and three finger widths distance into the body). This creates a heavy feeling that one can draw from in an upward direction through the top of the head. The spine is lengthened in this way, or you can say the bones are drawn out in an upward direction.

In a similar way the body is opened laterally - so the upper body feels broader. The arms are lengthened away from the spine, through the shoulder, elbow, wrist and finger joints and out beyond the fingers.

All of this is achieved using the mind because it is important to extend in a linear way, outwards and upwards simultaneously. After you have done this the body feels expanded and is relaxed into this expanded state.
Bristol 15.1.09