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From Wikipedia, the free encyclopedia

The human rib cage. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)

In vertebrate anatomy, ribs (Latin costae) are the long curved bones which form the ribcage. In most vertebrates, ribs surround the chest (Greek:θώραξ, Latin thorax) they enable lungs to expand by expanding the chest, they also protect the lungs, heart, and other internal organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.


Human anatomy

X-ray image of human chest, with ribs labeled.
Single human rib-detail

Humans have 24 ribs (12 pairs). The first seven sets of ribs, known as "true ribs", are directly attached to the sternum through the costal cartilage. The following five sets are known as "false ribs", three of these sharing a common cartilaginous connection to the sternum, while the last two (eleventh and twelfth ribs) are termed floating ribs (costae fluitantes) or vertebral ribs. They are attached to the vertebrae only, and not to the sternum or cartilage coming off of the sternum. Some people are missing one of the two pairs of floating ribs, while others have a third pair. Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.

The ribcage is separated from the lower abdomen by the thoracic diaphragm which controls breathing. When the diaphragm contracts, the ribcage and thoracic cavity are expanded, reducing intra-thoracic pressure and drawing air into the lungs.

In other animals

In fish, there are often two sets of ribs attached to the vertebral column. One set, the dorsal ribs, are found in the dividing septum between the upper and lower parts of the main muscle segments, projecting roughly sideways from the vertebral column. The second set, of ventral ribs arise from the vertebral column just below the dorsal ribs, and enclose the lower body, often joining at the tips. Not all species possess both types of rib, with the dorsal ribs being most commonly absent. Sharks, for example, have no dorsal ribs, and only very short ventral ribs, while lampreys have no ribs at all. In some teleosts, there may be additional rib-like bones within the muscle mass.[1]

Skeleton of a dog showing the location of the ribs

Tetrapods, however, only ever have a single set of ribs which are probably homologous with the dorsal ribs of fishes. In the early tetrapods, every vertebra bore a pair of ribs, although those on the thoracic vertebrae are typically the longest. The sacral ribs were stout and short, since they formed part of the pelvis, connecting the backbone to the hip bones.[1]

In most subsequent forms, many of these early ribs have been lost, and in living amphibians and reptiles, there is great variation in rib structure and number. For example, turtles have only eight pairs of ribs, which are developed into a bony or cartilagenous carapace and plastron, while snakes have numerous ribs running along the full length of their trunk. Frogs typically have no ribs, aside from a sacral pair, which form part of the pelvis.[1]

In birds, ribs are present as distinct bones only on the thoracic region, although small fused ribs are present on the cervical vertebrae. The thoracic ribs of birds possess a wide projection to the rear; this uncinate process is an attachment for the shoulder muscles.[1]

Mammals usually also only have distinct ribs on the thoracic vertebra, although fixed cervical ribs are also present in monotremes. In marsupials and placental mammals, the cervical and lumbar ribs are found only as tiny remnants fused to the vertebrae, where they are referred to as transverse processes. In general, the structure and number of the true ribs in humans is similar to that in other mammals. Unlike reptiles, caudal ribs are never found in mammals.[1]

See also


  1. ^ a b c d e Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 170–173. ISBN 0-03-910284-X.  
  • Clinically Oriented Anatomy, 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

RIB (from O. Eng. ribb; the word appears in many Teutonic languages, cf. Ger. Rippe, Swed. reb), in anatomy, the primary meaning, one of the series of elastic arched bones (costae) which form the casing or framework of the thorax (see Skeleton: Axial). The word is in meaning transferred to many objects resembling a rib in shape or function. In architecture, it is thus used of the arches of stone which in medieval work constitute the skeleton of the vault, and carry the shell or web. Although in the Roman vault the rih played an important element in its construction, it was generally hidden in the thickness of the vault and was made subservient to its geometrical surfaces. The Gothic masons, on the other hand, reversed the process, and not only made the vaulting surface subservient to the rib, but by mouldings rendered the latter a highly decorative feature. The principal ribs are the transverse (arc double au), the diagonal (arc ogive) and the wall rib (f ormeret) . Those of less importance are the intermediate, the ridge and lierne ribs. The ridge-rib is one first introduced into the vault to resist the thrust of the intermediate ribs between the wall and diagonal ribs; it also served to mark the junction of the filling-in or web of vaults in those cases where the courses dipped toward the diagonal rib. (See Vault.) A lierne rib (the term is borrowed from the French) is a short rib, introduced into the vaulting in the Early Perpendicular period, which coupled together the transverse and intermediate ribs; in the later period the "lierne" rib becomes one of the chief features of the "Stella" vault (see further Vault).

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rib (plural ribs)

  1. Any of a series of long curved bones occurring in 12 pairs in humans and other animals and extending from the spine to or toward the sternum
  2. A part or piece, similar to a rib, and serving to shape or support something
  3. A cut of meat enclosing one or more rib bones
  4. (nautical) Any of several curved members attached to a ship's keel and extending upward and outward to form the framework of the hull
  5. Any of several transverse pieces that provide an aircraft wing with shape and strength
  6. (architecture) A long, narrow, usually arched member projecting from the surface of a structure, especially such a member separating the webs of a vault
  7. A raised ridge in knitted material or in cloth
  8. (botany) The main, or any of the prominent veins of a leaf
  9. A teasing joke
  10. (Irish) (colloquial) A single strand of hair.
  11. A stalk of celery.



to rib

Third person singular

Simple past

Past participle

Present participle

to rib (third-person singular simple present ribs, present participle ribbing, simple past and past participle ribbed)

  1. To shape, support, or provide something with a rib or ribs
  2. To tease or make fun of someone

Derived terms



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