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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.
Pronunciation/ˈkɒksɪks/ KOK-siks
Latinos coccygis
Anatomical terms of bone

The coccyx (pl: 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 horses. In tailless primates (e.g. humans and other 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.

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  • ✪ Most USELESS Human Body Parts!
  • ✪ Why Don't Humans Have Tails?
  • ✪ Why Some Humans Are Born With Tails
  • ✪ 5 Most Shocking Genetic Mutations In Humans
  • ✪ How Humans Lost Their Tails — HHMI BioInteractive Video


From wisdom teeth to your tailbone, here are 13 of the most useless body parts! 13. Wisdom Teeth Wisdom teeth are the third and final set of molars that most people get in their late teens or early twenties. With all the money spent on removing them and all the pain that one has to endure during the process, it’s frustrating to know that wisdom teeth don’t serve any practical purpose. They are simply the remnants our ancestors’ teeth, who had larger jaws than we currently do. The reason why wisdom teeth have no use anymore is because human jaws have become smaller as they evolved, leaving little space for wisdom teeth to grow in comfortably. Another theory suggests that early humans used to lose their teeth quickly as they aged, so wisdom teeth could take the place of lost teeth and allow them to eat normally (and thus survive) for longer. Now they just cause all kinds of problems if they are misaligned such as jaw and nerve damage as well as infections that can be extremely painful. 12. Body Hair and Arrector Pili We all know about body hair, but what exactly are arrector pili? These are the smooth muscle fibers that give humans the peculiar sensation we commonly call “goose bumps”. If the arrector pili are activated, hair that come out of the nearby follicles stands up, giving us those famous goose bumps on our skin. Goose bumps are important to certain animals (like cats), which use those hairs on the body to swell up and make themselves look ‘bigger’ than they actually are. But human body hair is so small and fine that it does little more than give us a shiver, or let us know that something is frightening us! Yes, you can say that body hair protects us from the cold, and the hair on our head may help you look stylish, but that’s about it for legitimate functions of human body hair and arrector pili. 11. Eyebrows The evolutionary purpose of eyebrows is debatable: In one camp, scientists believe brows keep sweat and rain off your eyes, which would help in primitive hunting and navigation. Moreover, diverting the sweat away is also beneficial as the salt in sweat irritates the eyes, making them sting. Other scientists favor the hypothesis that eyebrows serve to communicate your emotions, but they may also communicate your identity. Behavioral neuroscientists from MIT found that people were less likely to recognize pictures of celebrities without their eyebrows than without their eyes. The researchers speculate that eyebrows have remained because they’re crucial to identifying faces and navigating social circumstances. 10. Tailbone/Coccyx Although we don’t sport these animalian appendages anymore, our ancestors once had tails. Tails were used to maintain balance while we walked, but as the human body evolved, the need for a tail disappeared. The tailbone, or coccyx, is situated at the end of the spinal cord. When we did have tails, this part of our anatomy was vital to our survival and balance. However, as tails disappeared, so did the functions of the tailbone. While we don’t really need it, it has been suggested that the coccyx helps to anchor minor muscles and may support the pelvic organs, so, it’s better to not underestimate its existence in the human body. 9, Male Nipples This has been a topic of significant discussion over the years, and has sparked all kinds of weird arguments, one even stating that ‘men have descended from women’. This isn’t true, but if you want to know the real reason behind male nipples, one has to go pretty far back, all the way to your time as a fetus. Both men and women have nipples because in the early stages of fetal development, an unborn child is effectively sexless meaning it has no gender yet. Thus, nipples are present on both males and females. During the later stages of fetal development, it is ‘testosterone’, a hormone, that decides the gender of the fetus – either male or female. It should be noted that certain males have been found to lactate and there have been numerous cases of breast cancer in males. 8, Third Eyelid This is the part of the eye that you can see at the corner of the eye (next to the tear duct). Although certain animals, like dogs, reptiles and fish, need it for a variety of functions and protected vision, humans do not need this third eyelid to maintain proper vision or survival. This doesn’t mean that the third eyelid does nothing and just sits there. When we move our eyes, the third eyelid (plica semilunaris) ensures proper tear drainage and sweeps debris away from the eye. For anyone who has ever walked along a windy beach, we can appreciate that particular function, right? 7. Darwin’s Point Around the sixth week of gestation, six swellings of tissue called the Hillocks of Hiss arise around the area that will form the ear canal. These eventually come together to form the outer ear. Darwin’s point, or tubercle, is a minor malformation of the junction of the fourth and fifth Hillocks of Hiss. It is found in a minority of people and takes the form of a node or bump on the rim of their outer ear, which is thought to be the vestige of a joint that allowed the top part of the ancestral ear to swivel or flop down over the opening to the ear. Technically considered a defect, Darwin’s point does no harm and is surgically removed for cosmetic reasons only. However, the genetics behind it tells an interesting tale. The trait is passed on according to an autosomal dominant pattern, meaning that a child needs to only inherit one copy of the gene responsible to have Darwin’s point. That suggests that at one time it was useful. However, it also has variable penetration, meaning that you won’t necessarily have the trait even if you inherit the gene. 6. Philtrum No, that little indent under your nose isn’t there to make it difficult to apply lipstick in the dark, but it doesn’t serve any other purpose either. The indent, called the philtrum, is just a residual reminder of your time in the womb: in utero, the two sides of your face develop independent of one another, then join at the middle. When the two sides fail to fuse properly, the result is a cleft palate, which occurs in about 1 of every 750 births. Ancient Romans found the philtrum erotic, and named that dip in the upper lip the “Cupid’s Bow.” In fact, the word philtrum comes from a Greek term meaning “love potion.” If you’ve seen makeup tutorials on YouTube, you will know that women still highlight their cupid’s bow to emphasize it, but they may not know exactly why! 2000 years later, it’s still sexy! 5. Auricular muscles The auricular, or extrinsic, muscles of the human ear include the anterior auricular muscle, the superior auricular muscle, and the posterior auricular muscle. Together, they control the pinna, or the visible part of the ear. In many mammals, ear movements produced by the auricular muscles play a role in sound localization and the expression of emotion. You must have noticed your pets perking up their ears when startled or lay them back flat if they are listening or embarrassed. These extrinsic ear muscles are used to perk up their ears as a sign of alertness or to move them around according to motion of predators or prey. But in humans, the muscles are considered nonfunctional. Darwin proposed that humans effectively capture sounds by positioning the head to receive them, thereby compensating for the loss of or eliminating the need for the auricular muscles. Through repeated effort, however, humans can recover some ability to wiggle their ears, if that is a goal of yours. 4. Fifth Toe Have you often been injured by furniture, especially on that all too useless pinky toe? You are not the only one then who has been exposed to it being more of a disadvantage! Used primarily by primates and our tree hugging ancestors for clinging and swinging off branches, they have greatly reduced in size now and have become entirely obsolete. Not required for balance, or mobility in any way; the fifth toe is a body part we don’t really need. Several mammals have already lost their digits thanks to evolution such as cows, horses, pigs and camels and have hooves instead. If humans were to follow and lose their pinky toe, it wouldn’t make much difference except maybe much better fitting shoes! 3. Tonsils One of the most removed organs, tonsils are basically collections of lymphoid tissue, one on each side of the back of the throat. They do function as a part of your immune system fighting infections as the first in line for defence in the throat. The major problem with its bacteria fighting effect is its tendency to get sore and inflamed and get recurring infections. If the infection is virus initiated, antibiotics don’t help and doctors almost always recommend getting tonsil removal surgery called a tonsillectomy. So for many people the tonsils aren’t even that helpful to begin with! 2. Chins Who knew a body part could be such a hot topic? It turns out there are endless debates when it comes to whether or not the chin has a purpose. It becomes even stranger when you consider that among all the primates – including our extinct relatives – only we have chins. Chimpanzee and ape jaws slant inwards for instance. Even our closest extinct relatives such as Neanderthals did not have them. Nobody seems to know why – although over the last century several theories as to its purpose have been offered. To start with it has long been proposed that our chin may help us chew food. The theory goes that we need the extra bone to deal with the stresses involved with chewing. However, this idea falls flat when you compare us to other great apes with similar-shaped jaws. When we chew, our jaw gets pulled apart a bit like a wishbone and the further apart our jaws are the weaker the bones are. If we were to protect ourselves from the stresses of chewing we would need more bone on the inner wall of the jaw near the tongue, not beneath our jaw. That's exactly what you see in chimpanzees and macaques. They have extra bone on the tongue-ward side of their lower jaw, called a "simian shelf", which we do not have. The added bone that forms our chin is not very useful for additional chewing strength. While it has no obvious function, it might simply be there because we like it—the result of sexual selection. While some experts believe that the chin helps us control the forces our jaw produces when we chew, the Iowa Facial Growth Study determined that "chins are unlikely related to the need to dissipate stresses and strains." 1. Appendix This is an organ located at the junction of the large and small intestines. Since it is connected to the intestines, many people think it plays some role in the digestive process, but it serves no purpose whatsoever. At least, as far as we know. The main function of the appendix in other species is to aid in digestion for diets that are largely herbivorous. This is why the appendix is an important part of digestion in plant-eating vertebrates. But in humans, it doesn’t seem to do anything. A study in 2009 showed some signs that the appendix may store good bacteria that can help people suffering from digestion issues. But so does the small intestine. Most medical practitioners believe it is a useless part left over from our evolutionary past. What we do know, is that it can become inflamed and rupture. In severe cases of appendicitis it has to be removed or you can die! Pretty scary for something that is just sitting in your body doing nothing the rest of the time. There are no known health problems from having your appendix removed. Thanks for watching! Remember to subscribe and click here for more videos! See you next time! Bye!



A coccyx with four vertebrae below the sacrum.
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]


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.


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.


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]


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.


It has been claimed that the coccyx is not entirely useless in humans,[11] based on the fact that the coccyx has attachments to various muscles, tendons and ligaments. However, these muscles, tendons and ligaments are also attached at many other points, to stronger structures than the coccyx. The claim that the coccyx attachments are important to the well-being of humans is cast into doubt by the large number of cases of coccygectomy for coccydynia. Reviews of studies covering more than 700 operations found the operation was successful in relieving pain in 84% of cases.[12][13] These studies did not identify any disadvantage to patients caused by the absence of a coccyx.

Clinical significance

Injuring the coccyx can give rise to a painful condition called coccydynia and one or more of the bones or the connections thereof may be broken, fractured tailbone.[14] [15] A number of tumors are known to involve the coccyx; of these, the most common is sacrococcygeal teratoma. Both coccydynia and coccygeal tumors may require surgical removal of the coccyx (coccygectomy). One very rare complication of coccygectomy is a type of perineal hernia known as a coccygeal hernia.[16]



The term coccyx is derived from the ancient Greek word κόκκυξ[17][18] kokkyx "cuckoo";[19] the latter is attested in the writings of the Greek physician Herophilus to denote the end of the vertebral column.[20] This Greek name for the cuckoo was applied as the last three or four bones of the coccyx resemble the beak of this bird,[17][20][21][22] when viewed from the side.[9][23]

This established etymological explanation can also be found in the writings of the 16th century anatomist Andreas Vesalius who wrote: os cuculi, a similitudine rostri cuculi avis [20] (the cuckoo bone shows a likeness to the beak of the cuckoo bird). Vesalius used the Latin expression os cuculi, with os, bone[24] and cuculus, the Latin name for the cuckoo.[24] The 16th/17th century French anatomist Jean Riolan the Younger gives a rather hilarious etymological explanation, as he writes: quia crepitus, qui per sedimentum exeunt, ad is os allisi, cuculi vocis similitudinem effingunt [20] (because the sound of the farts that leave the anus and dash against this bone, shows a likeness to the call of the cuckoo). The latter is not considered as potential candidate.[20][21]

Besides os cuculi, os caudae,[20][25] with caudae, of the tail[24] is attested. This Latin expression might be the source of the English, French language, German and Dutch terms tailbone, l'os de la queue,[25] Schwanzbein [21][25] and staartbeen.[26] In the current official anatomic Latin nomenclature, Terminologia Anatomica,[27] coccyx and os coccygis is used.

Additional images

See also


  1. ^ Nakatsukasa 2004, Acquisition of bipedalism (See Fig. 5 entitled First coccygeal/caudal vertebra in short-tailed or tailless primates..)
  2. ^ Note: Nacholapithecus and Nakaliphitecus nakayamai are two different species of Miocene hominoids (specimens from Nakali and Nachola respectively). See for example "Comparisons with Other Hominoids" in (Kunimatsu, Nakatsukasa et al. Dec 2007)
  3. ^ Postacchini F; Massobrio M] (October 1983). "Idiopathic coccygodynia. Analysis of 51 operative cases and a radiographic study of the normal coccyx". The Journal of Bone and Joint Surgery. American Volume (65(8)): 1116–1124.
  4. ^ Kim NH, Suk KS (June 1999). "Clinical and radiological differences between traumatic and idiopathic coccygodynia". Yonsei Medical Journal. 40 (3): 215–220. doi:10.3349/ymj.1999.40.3.215. PMID 10412331.
  5. ^ Cosmo, L. (2017). "Filling the Gap: on the New Micro-toponomic Phenomena and Partial Topologies". Health Research. 1 (1): 39-49. doi:10.31058/
  6. ^ Lierse, Werner (2012-12-06). Applied anatomy of the pelvis. p. 40. ISBN 9783642713682.
  7. ^ Maigne JY; Molinie V; Fautrel B. (1992). "Anatomie des disques coccygiens". Revue de Médecine Orthopedique. 28: 34–35.
  8. ^ Saluja PG. (1988). "The incidence of ossification of the sacrococcygeal joint". Journal of Anatomy. 156: 11–15.
  9. ^ a b c d Foye, Patrick M; Buttaci, Charles J (June 3, 2008). "Coccyx Pain". eMedicine.
  10. ^ Morris, Craig E. (2005). Low Back Syndromes: Integrated Clinical Management. McGraw-Hill. p. 59. ISBN 978-0-07-137472-9.
  11. ^ Saladin, Kenneth S. (2003). 3rd (ed.). Anatomy & Physiology: The Unity of Form and Function. McGraw-Hill. p. 268.
  12. ^ Coccygektomi kan være en behandlingsmulighed ved kronisk coccygodyni (Coccygectomy may be a treatment option for chronic coccydynia) Ugeskr Læger 2011 Feb 14; 173(7): 495-500. In Danish. Aarby, Nanett Skjellerup (1), Trollegaard, Anton Mitchell (2) and Hellberg, Steen (2)
  13. ^ Coccygodynia and Coccygectomy. Heum Dai Kwon et al., Korean Journal of Spine, 9, 4 (2012), 326-333.
  14. ^ Maigne, J-Y; Doursounian, L; Chatellier, G.] (2000). "Causes and Mechanisms of Common Coccydynia. Spine". 25 (23). 3072–3079. Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  15. ^ Foye P, Buttaci C, Stitik T, Yonclas P (2006). "Successful injection for coccyx pain". Am J Phys Med Rehabil. 85 (9): 783–784. doi:10.1097/01.phm.0000233174.86070.63. PMID 16924191.
  16. ^ Miranda EP, Anderson AL, Dosanjh AS, Lee CK (September 2007). "Successful management of recurrent coccygeal hernia with the de-epithelialised rectus abdominis musculocutaneous flap". J Plast Reconstr Aesthet Surg. 62 (1): 98–101. doi:10.1016/j.bjps.2007.08.002. PMID 17889632.
  17. ^ a b Klein, E. (1971). A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture. Amsterdam: Elsevier Science B.V.
  18. ^ Harper, Douglas. "coccyx". Online Etymology Dictionary.
  19. ^ κόκκυξ. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  20. ^ a b c d e f Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  21. ^ a b c Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
  22. ^ Panourias, I.G., Stranjalis, G., Stavrinou, L.C. & Sakas, D.E. (2011). The Hellenic and Hippocratic origins of the spinal terminology. Journal of the History of the Neurosciences, 20, 177-187.
  23. ^ Sugar, Oscar (February 1995). "Historical Perspective Coccyx: The Bone Named for a Bird". Spine. 20 (3): 379–383. doi:10.1097/00007632-199502000-00024. ISSN 0362-2436. PMID 7732478.
  24. ^ a b c os, cuculus, cauda. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  25. ^ a b c Schreger, C.H.Th.(1805). Synonymia anatomica. Synonymik der anatomischen Nomenclatur. Fürth: im Bureau für Literatur.
  26. ^ Everdingen, J.J.E. van, Eerenbeemt, A.M.M. van den (2012). Pinkhof Geneeskundig woordenboek (12de druk). Houten: Bohn Stafleu Van Loghum.
  27. ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme

Further reading

External links

This page was last edited on 14 September 2019, at 13:29
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