Which bony structure is NOT involved in the process of breathing?

The femur is not involved in the process of breathing because it is a long bone located in the thigh, providing support for locomotion and mobility of the lower limb. In contrast, the thoracic spine, ribs, and sternum are components of the thoracic cage, which plays a critical role in respiration. The thoracic spine supports the structures of the thorax and allows for the attachment of the ribs. The ribs form a protective cage around the lungs and heart; their movement helps expand and contract the thoracic cavity during breathing. The sternum serves as an anchor for the ribs and also facilitates their movement. Therefore, the femur does not participate in any of the mechanics of inhalation or exhalation, making it the correct choice for this question.