Which part of the rib articulates with the transverse process of the thoracic vertebra?

The tubercle of the rib is the specific part that articulates with the transverse process of the thoracic vertebra. This articulation is an important aspect of the rib's connection to the spine. The tubercle has a facet that is designed to fit into the transverse process, forming a joint that allows for some movement and contributes to the overall flexibility of the thoracic cage during respiration.

The head of the rib connects with the vertebral body at the costovertebral joint, and the neck is simply a narrow region between the head and tubercle, not involved directly in articulation with the transverse process. The shaft of the rib extends from the tubercle and forms the bulk of the rib structure, primarily serving as a protective barrier for the thoracic cavity rather than participating in vertebral articulation. Hence, the correct answer highlights the specific anatomical feature that fulfills the articulation function with the thoracic vertebra's transverse process.