Coccyx - Stiffness

Japanese: 尾骨 - びこつ

This refers to fused caudal vertebrae. As the name suggests, in vertebrate animals, the spinal column made up of vertebrae (vertebrae) supports the body. This column is named according to its parts, with the rear end being called the caudal vertebrae. In some primates such as humans, these caudal vertebrae are fused to form the tailbone (also called the coccyx). In tailless animals such as humans, the tailbone is a vestigial organ. Birds and amphibians may also have fused tips of the caudal vertebrae, but this is distinguished from the fused tailbone, which is called the pygostyle.

[Masaru Wada]

Coccyx in humans

Located at the very end of the spine, these are small bones that follow the sacrum and consist of 3 to 6 (usually 4) caudal vertebrae. They lack a vertebral arch and barely retain the shape of a vertebra, becoming smaller and smaller as they move downwards. As a whole, they are fused together to form small, spherical or slightly long bone fragments. During the fetal stage, nine caudal vertebrae are found, but they gradually disappear during development.

[Kazuyo Shimai]

[Reference] | Tail | Spine

Names of parts of the spine
©Shogakukan ">

Names of parts of the spine

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

尾椎(びつい)の融合したものをいう。脊椎(せきつい)動物では、その名前の示すように脊椎（椎骨）からなる脊柱が体を支えている。この脊柱はその部分によって名前がつけられており、後端の部分を尾椎とよぶ。ヒトなどの霊長類のなかには、この尾椎が融合して尾骨（尾骶骨(びていこつ)ともいう）を形成する場合がある。ヒトのような尾のない動物では尾骨は痕跡(こんせき)器官である。鳥類や両生類でも尾椎の先端が融合している場合があるが、これは尾端骨といって区別している。

［和田　勝］