Final answer:
The nail bed is attached to the phalanx bones of the fingers and toes, not to the larger bones such as the femur, tibia, radius, or ulna. The nail bed supports the nail plate and nails are made of keratin.
Step-by-step explanation:
The nail bed is attached to the bones at the tips of the fingers and toes, specifically the phalanges, also known as phalanx bones. These are not directly related to the larger bones listed in the options provided like the femur, tibia, radius, or ulna. Moreover, it is important to clarify that the nail bed is not the middle portion of the hard nail plate but rather the skin underneath the nail plate that supports it. Furthermore, nails are primarily composed of a tough protein called keratin, which is also found in hair and the outer layer of skin.