Coccyx

Coccyx
Coccyx - anterior view02.png
The coccyx
Illu vertebral column.jpg
The coccyx is the final bone in the vertebral column that surrounds the spinal cord.
Details
Pronunciations/ KOK-siks
Identifiers
Latinos coccygis
MeSHD003050
TAA02.2.06.001
FMA20229
Anatomical terms of bone

The coccyx, commonly referred to as the tailbone, is the final segment of the vertebral column in humans and apes, and certain other mammals such as horses. In humans and other tailless primates (e.g., great apes) since Nacholapithecus (a Miocene hominoid),[1][2] the coccyx is the remnant of a vestigial tail. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan.It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.

Structure

A coccyx with four vertebrae below the sacrum.

The coccyx is formed of either three, four or five rudimentary vertebrae. It articulates superiorly with the sacrum. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. The transverse processes are most prominent and noticeable on the first coccygeal segment. All the segments lack pedicles, laminae and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the remaining ones diminish in size from above downward.

Most anatomy books incorrectly state that the coccyx is normally fused in adults. In fact it has been shown that the coccyx may consist of up to five separate bony segments, the most common configuration being two or three segments.[3][4]

Surfaces

The anterior surface is slightly concave and marked with three transverse grooves that indicate the junctions of the different segments. It gives attachment to the anterior sacrococcygeal ligament and the levatores ani and supports part of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles–the rudimentary articular processes of the coccygeal vertebrae. Of these, the superior pair are the largest, and are called the coccygeal cornua they project upward, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve.

Borders

The lateral borders are thin and exhibit a series of small eminences, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened from before backward, and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the anterior division of the fifth sacral nerve; the others diminish in size from above downward, and are often wanting. The borders of the coccyx are narrow, and give attachment on either side to the sacrotuberous and sacrospinous ligaments, to the coccygeus and levator ani in front of the ligaments, and to the gluteus maximus behind them.

Apex

The apex is rounded, and has attached to it the tendon of the external anal sphincter. It may be bifid (divided into two).

Coccygeal fossa

The coccygeal fossa is a shallow depression (fossa) on the surface between the sacrum and the perineum, located in the intergluteal cleft that runs from just below the sacrum to the perineum.[5] It does not always appear. The coccygeal fossa marks the deepest part of the pelvic floor, next to the coccyx. The levator ani ascends from here.[6]

Extensor coccygis

The extensor coccygis is a slender muscle fascicle, which is not always present. It extends over the lower part of the posterior surface of the sacrum and coccyx. It arises by tendinous fibers from the last segment of the sacrum, or first piece of the coccyx, and passes downward to be inserted into the lower part of the coccyx. It is a rudiment of the extensor muscle of the caudal vertebrae of other animals.

Sacrococcygeal and intercoccygeal joints

The joints are variable and may be: (1) synovial joints; (2) thin discs of fibrocartilage; (3) intermediate between these two; (4) ossified.[7][8]

Attachments

The anterior side of the coccyx has attachments to the levator ani muscle, coccygeus, iliococcygeus, and pubococcygeus, anococcygeal raphe. Attached to the posterior side is the gluteus maximus, which extends the thigh at the hip joint.[9] The ligaments attached to the coccyx include the anterior and posterior sacrococcygeal ligaments which are the continuations of the anterior and posterior longitudinal ligaments that stretches along the entire spine.[9] The lateral sacrococcygeal ligaments complete the foramina for the last sacral nerve.[10] Some fibers of the sacrospinous and sacrotuberous ligaments (arising from the spine of the ischium and the ischial tuberosity respectively) also attach to the coccyx.[9] An extension of the pia mater, the filum terminale, extends from the apex of the conus, and inserts on the coccyx.

Other Languages
العربية: عصعص
azərbaycanca: Büzdüm sümüyü
Bân-lâm-gú: Bí-lû-kut
беларуская: Хвасцец
български: Опашна кост
bosanski: Trtična kost
brezhoneg: Askorn belost
català: Còccix
Чӑвашла: Сутана
čeština: Kostrč
dansk: Haleben
Deutsch: Steißbein
español: Coxis
Esperanto: Kokcigo
euskara: Kokzix
فارسی: دنبالچه
français: Coccyx
Gaeilge: Gimide
galego: Cóccix
한국어: 꼬리뼈
Ido: Kocigo
Bahasa Indonesia: Tulang sulbi
italiano: Coccige
עברית: עצם העוקץ
қазақша: Құйымшақ
кырык мары: Пачтамга
latviešu: Astes kauls
lietuvių: Uodegikaulis
Bahasa Melayu: Koksiks
Nederlands: Stuit
नेपाल भाषा: कक्सिक्स्
日本語: 尾骨
norsk: Halebein
português: Cóccix
română: Coccis
русский: Копчик
Scots: Coccyx
sicilianu: Cruduzzu
Simple English: Coccyx
slovenčina: Kostrč
slovenščina: Trtica
کوردی: کلێجە
suomi: Häntäluu
українська: Куприкова кістка
粵語: 尾龍骨
中文: 尾骨