Are bones superficial to muscles?
Bones are deep to muscles. Muscles are superficial to bones.
In the way you are using "superficial" it will mean " being on or near the surface". Thus the answer is "YES" the skin is a superficial organ - BUT - "NO" the skin is not "superficial" specifically to muscles - it does not surround muscles, it surrounds the whole body and the muscles are beneath (and some in - the ones that raise the hairs) the skin.