The hyoid bone is the only bone in the human body not connected to any other.

 

This small U-shaped bone can be found amid the muscles of a human neck. Insignificant as it may seem, it serves a VERY important purpose: the hyoid bone allows human beings to speak! It helps to support your tongue and raise your larynx whenever you talk and swallow. The hyoid exists in other animals also, but humans are the only species where the location of their hyoid bone permits it to work together with the tongue and larynx to articulate a large variety of distinct sounds

The small bones in our ear (the hammer, the anvil, and the stirrup) are also not connected to the rest of the skeletal system, but they are at least attached to each other. These bones connect the ear drum to the cochlea (which transmits sound to the brain). They are necessary to convert vibrations of the eardrum into the fluid of the inner ear so that we can perceive those vibrations as sound.