What term describes muscle fibers that are directly affixed to the bone?

The correct term describing muscle fibers that are directly affixed to the bone is "fleshy." This refers to the type of muscle attachment where muscle fibers are connected directly to the periosteum of the bone without an intervening tendon. This direct attachment allows for efficient force transmission from the muscle to the bone during movement.

The other terms relate to different aspects of muscle and tissue structure. Tendinous attachment refers to muscles that connect to bones via tendons, which are dense connective tissues. Elastic pertains to the ability of muscle or tissue to stretch and recoup, which does not specifically relate to how muscles attach to bones. Striated muscles refer to a type of muscle with a specific banded appearance under a microscope, commonly seen in skeletal muscles, but it does not denote their attachment to bones. Understanding these terms helps clarify the types of muscle attachments and their functional significance in the human body.