UBPROP:0000106

Note that in TAO, ribs are numbered by *vertebrae*

uberon

rib_number

http://purl.obolibrary.org/obo/UBERON_0002228

true

http://purl.obolibrary.org/obo/BSPO_0000096

rib_number

In the early tetrapods, every vertebra bore a pair of ribs, although those on the thoracic vertebrae are typically the longest. In most subsequent forms, many of these early ribs have been lost, and in living amphibians and reptiles, there is great variation in rib structure and number. For example, turtles have only eight pairs of ribs, which are developed into a bony or cartilagenous carapace and plastron, while snakes have numerous ribs running along the full length of their trunk. Frogs typically have no ribs, aside from a sacral pair, which form part of the pelvis. Mammals usually also only have distinct ribs on the thoracic vertebra, although fixed cervical ribs are also present in monotremes. In marsupials and placental mammals, the cervical and lumbar ribs are found only as tiny remnants fused to the vertebrae, where they are referred to as transverse processes. In general, the structure and number of the true ribs in humans is similar to that in other mammals. Unlike reptiles, caudal ribs are never found in mammals.