Final answer:
Ribs are curved bones that articulate with thoracic vertebrae. The student is referring to specific anatomical variations in the ribs and sacrum.
Step-by-step explanation:
Ribs are flattened, curved bones that are numbered 1-12. The head of the rib articulates with the costal facets on the thoracic vertebrae, while the rib tubercle articulates with the facet on the vertebral transverse process. In this case, the student is mentioning a riblet on the right at T12 and left sacralization. These terms are describing anatomical variations and abnormalities in the ribs and sacrum.