Rib - 13

The thirteenth rib is part of the asternal ribs in most species. It articulates dorsally with the thirteenth thoracic vertebra and its costal cartilage fuses with that of the previous rib, thus allowing the formation of the costal arch.

Variation:

In dogs and cats, it is the last rib and is floating. Its costal tubercle is completely erased. The rib therefore articulates only with the cranial costal facet of the corresponding vertebra.