Take a look at Rodin's "The Thinker" -- his elbow on his knee, his wrist on his jaw.  All of these are corner points of the body.

Babe Lab would like to suggest that these corners are where parts of our bodies naturally go to be at rest.  The bone is closest to the skin at these points, giving us someplace sturdy to apply weight, or hook ourselves around.  There is nowhere we can slip.  

[below] A cross-armed girl's hands settle snugly to the inner elbows (corners).

[above] A hand planted on the corner of the hip...

[below] ...or a foot nestled just above the ankle of the opposite leg...

[below] ...or in the hollow of the knee convey security and stability.

Watch your own posture when you settle.  Are you currently at rest on any of your body's corner points?