Synovial joint - Synovial joint

…the first type is when both bones (or cartilages) are connected only by ligaments (syndesmoses), such as the joints of bones other than the vertebral column in fish, the hinge-like joints found in the carapace and plastron of some turtles, and the dorsal and ventral joints of avian ribs, but is extremely rare in humans (such as the distal ends of the tibia and fibula). The second type is called a synovial joint, in which both bone ends are covered with cartilage (articular cartilage), there is a gap (articular cavity) between them filled with mucus (synovial fluid), and the entire joint is enclosed by a sac of connective tissue (joint capsule) (in human anatomy, this type of joint is called a "joint" in the strict sense). In the joint cavity, there may be a thin disk-shaped cartilage (articular disc) or a ring-shaped or crescent-shaped cartilage (articular meniscus), which serves to facilitate the fitting and sliding of the joint surfaces. …

*Some of the terminology that refers to "synovial joint" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…一つは両方の骨(または軟骨)が靱帯だけで結びつけられている場合(靱帯結合)で，魚類における脊柱以外の骨の連結，ある種のカメの背甲や腹甲に見られるちょうつがい状の関節，鳥類の肋骨の背側部と腹側部の連結などがそれにあたるが，人体ではきわめてまれである(脛骨と腓骨の遠位端どうしなど)。もう一つは滑膜性結合とよばれるもので，両方の骨端が軟骨(関節軟骨)に覆われ，それらの間にすきま(関節腔)があって粘液(滑液)を満たし，その連結部全体が結合組織性の袋(関節包)で包まれている場合である(人体解剖学ではこの種の連結を厳密な意味での〈関節〉とする)。関節腔の中には薄い円板状の軟骨(関節円板)や環状または三日月型の軟骨(関節半月)が挟まっている場合があり，これらは関節面どうしの適合とすべりを円滑にする働きをもっている。…

※「滑膜性結合」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報