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Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caudal vertebrae bear ribs, the caudal ribs, though these are often fused with the vertebrae. [1]
The vertebrae fit together in a ball-and-socket articulation, in which the convex articular feature of an anterior vertebra acts as the ball to the socket of a caudal vertebra. [25] This type of connection permits a wide range of motion in most directions, while still protecting the underlying nerve cord.
A haemal arch, also known as a chevron, is a bony arch on the ventral side of a tail vertebra of a vertebrate. The canal formed by the space between the arch and the vertebral body is the haemal canal. A spinous ventral process emerging from the haemal arch is referred to as the haemal spine. Blood vessels to and from the tail run through the arch.
The free vertebrae immediately following the fused sacro-caudal vertebrae of the synsacrum are known as the caudal vertebrae. Birds have between five and eight free caudal vertebrae. [7] The caudal vertebrae provide structure to the tails of vertebrates and are homologous to the coccyx found in mammals lacking tails. [16]
Posterior to the synsacrum there are a few free caudal vertebrae, the last of which is the pygostyle to which the long, stiff tail feathers are attached. The central section of the synsacrum is swollen to accommodate the glycogen body, an organ whose function is as yet unclear but which may be associated with balance. [1]
Modern birds still develop longer caudal vertebrae in their embryonic state, which later fuse to form a pygostyle. There are two main types of pygostyle: [citation needed] one, found in Confuciusornithidae, Enantiornithes, and some other Mesozoic birds, as well as in some oviraptorosaurs like Nomingia, is long and rod- or dagger blade-like ...
[21] [22] Fewer than 40 cases have been reported of infants with "true tails" containing the caudal vertebrae, a result of atavism. [23] In 2024, scientists claimed to have found a genetic mutation that contributed to the loss of the tail in the common ancestor of humans and other apes. [24] [25]
In tetrapods, cervical vertebrae (sg.: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals ) lie caudal (toward the tail) of cervical vertebrae. [ 1 ]