Caudal vertebrae are the

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of the

tail The tail is the elongated section at the rear end of a bilaterian animal's body; in general, the term refers to a distinct, flexible appendage extending backwards from the midline of the torso. In vertebrate animals that evolution, evolved to los ...

in many vertebrates. In

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

, the last few caudal vertebrae fuse into the pygostyle, and in

apes Apes (collectively Hominoidea ) are a superfamily of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and Europe in prehistory, and counting humans are found glo ...

, including

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

, the caudal vertebrae are fused into the

coccyx The coccyx (: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horse anatomy, horses. In tailless primates (e.g. hum ...

. In many reptiles, some of the caudal vertebrae bear

ribs The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...

, the caudal ribs, though these are often fused with the vertebrae. The caudal vertebrae often articulate with haemal arches ventrally. The number of caudal vertebrae in animals can vary greatly. Anguid lizards have been reported to have as many as 111 caudal vertebrae, whereas as few as seven are present in the tail of the early therapsid '' Tapinocaninus''. In lepidosaurs and captorhinids, the caudal vertebrae possess fracture planes at mid-length that allow caudal autotomy. In frogs, the few caudal vertebrae are fused together to form part of the urostyle.

References

Skeletal system Vertebrate anatomy {{vertebrate-anatomy-stub