An animal with 7 cervical, 13 thoracic, and 6 lumbar vertebrae usually has how many pairs of ribs?

An animal with 7 cervical, 13 thoracic, and 6 lumbar vertebrae typically has a corresponding number of pairs of ribs that align with the thoracic vertebrae. In most mammals, each thoracic vertebra is associated with one pair of ribs. Therefore, with 13 thoracic vertebrae present, it is standard for the animal to have 13 pairs of ribs, one pair for each thoracic vertebra.

Ribs are classified as either true ribs, which directly connect to the sternum, or false ribs, which connect indirectly or not at all. The presence of additional lumbar vertebrae or cervical vertebrae does not affect the count of thoracic ribs. Given that the question focuses solely on the relationship between thoracic vertebrae and ribs, recognizing this direct correspondence provides a clear rationale for the 13 pairs of ribs associated with the 13 thoracic vertebrae.