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Detail of a single human rib
The human rib cage (Source: Gray's Anatomy of the Human Body , 20th ed. 1918)
Latin costae
MeSH D012272
TA A02.3.01.001
FMA 7574
Anatomical terminology

In vertebrate anatomy, ribs (Latin : costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to 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

Rib details

Ribs are classed as flat bones which usually have a protective role in the body. Humans have 24 ribs, in 12 pairs. All are attached at the back to the thoracic vertebrae, and are numbered from 1–12 according to the vertebrae they attach to. The first rib is attached to thoracic vertebra 1 (T1). At the front of the body most of the ribs are joined by costal cartilages to the sternum. The ribs connect to the vertebrae with two joints, the costovertebral joints.

The parts of a rib include the head, neck, body (or shaft), tubercle, and angle.

The head of the rib lies next to a vertebra. The ribs connect to the vertebrae with two costovertebral joints, one on the head and one on the neck. The head of the rib has a superior and an inferior articulating region, separated by a crest. These articulate with the superior and inferior costal facets on the connecting vertebrae. [1] The crest gives attachment to the intra-articulate ligament that joins the rib to the vertebra of the same number, at the intervertebral disc. Another ligament, the radiate ligament joins the head of the rib to the both the body of the upper vertebra and to the body of the lower vertebra. The smaller middle part of the ligament connects to the intervertebral disc. This plane joint is known as the articulation of the head of the rib.

The other costovertebral joint is that between the tubercle on the neck and the transverse process of the joining thoracic vertebra of the same rib number, and this is known as the costotransverse joint. The superior costotransverse ligament attaches from the non-articular facet of the tubercle to the transverse process of the vertebra.

The neck of the rib is a flattened part that extends laterally from the head. The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest (crista colli costae) for the attachment of the anterior costotransverse ligament; its lower border is rounded.

A tubercle of rib on the posterior surface of the neck of the rib, has two facets (surfaces) one articulating and one non-articulating. The articular facet, is small and oval and is the lower and more medial of the two, and connects to the transverse costal facet on the thoracic vertebra of the same rib number. [1] The transverse costal facet is on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs.

Rib cage

X-ray image of human chest, with ribs labelled Ribs labeled.png
X-ray image of human chest, with ribs labelled

The first seven sets of ribs, known as "true ribs", are attached to the sternum by the costal cartilages. The first rib is unique and easier to distinguish than other ribs. It is a short, flat, C-shaped bone. The vertebral attachment can be found just below the neck at the first thoracic vertebra, and the majority of this bone can be found above the level of the clavicle. Ribs 2 through 7 have a more traditional appearance and become longer and less curved as they progress downwards. [2] 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. They are attached to the vertebrae only, and not to the sternum or cartilage coming off of the sternum.

In general, human ribs increase in length from ribs 1 through 7 and decrease in length again through rib 12. Along with this change in size, the ribs become progressively oblique (slanted) from ribs 1 through 9, then less slanted through rib 12. [2]

The rib cage is separated from the lower abdomen by the thoracic diaphragm which controls breathing. When the diaphragm contracts, the thoracic cavity is expanded, reducing intra-thoracic pressure and drawing air into the lungs. This happens through one of two actions (or a mix of the two): when the lower ribs the diaphragm connects to are stabilized by muscles and the central tendon is mobile, when the muscle contracts the central tendon is drawn down, compressing the cavity underneath and expanding the thoracic cavity downward. When the central tendon is stabilized and the lower ribs are mobile, a contraction of the diaphragm elevates the ribs, which works in conjunction with other muscles to expand the thoracic indent upward.


Early in the developing embryo, somites form and soon subdivide into three mesodermal components – the myotome, dermatome, and the sclerotome. The vertebrae and ribs develop from the sclerotomes. [3]

During the fourth week (fertilization age) costal processes have formed on the vertebral bodies. These processes are small, lateral protrusions of mesenchyme that develop in association with the vertebral arches. During the fifth week the costal processes on the thoracic vertebrae become longer to form the ribs. In the sixth week, the costovertebral joints begin to develop and separate the ribs from the vertebrae. The first seven pairs of ribs, the true ribs join at the front to the sternal bars. By the fetal stage the sternal bars have completely fused. [3]

The ribs begin as cartilage that later ossifies – a process called endochondral ossification. Primary ossification centers are located near the angle of each rib, and ossification continues in the direction away from the head and neck. During adolescence secondary ossification centers are formed in the tubercles and heads of the ribs. [3]

Other animals

Skeleton of a dog showing the location of the ribs Dog anatomy lateral skeleton view.jpg
Skeleton of a dog showing the location of the ribs
Rib cage of the big brown bat (Eptesicus fuscus) Eptesicus fuscus ribcage.jpg
Rib cage of the big brown bat (Eptesicus fuscus)

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, the 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. [4]

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. [4]

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 cartilaginous 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. [4]

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. [4] Usually dogs have 26 ribs. 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. [4]

Ribs as food

Ribs as food are widely used from many animals. The ribs are the less meaty part of the meat chop and they are often cooked as part of a slab; five or more is known as a rack, as in a rack of lamb. Short ribs are ribs of beef either served singly or several as a plate. A rib steak from beef is a popular choice used in many cuisines. Pork ribs, including spare ribs are popular in European and Asian cuisine.

Additional images

See also

Related Research Articles

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In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine.

Rib cage arrangement of bones

The rib cage is the arrangement of ribs attached to the vertebral column and sternum in the thorax of most vertebrates, that encloses and protects the heart and lungs. In humans, the rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the shoulder girdle to form the core part of the human skeleton. A typical human rib cage consists of 24 ribs in 12 pairs, the sternum and xiphoid process, the costal cartilages, and the 12 thoracic vertebrae.

Clavicle plain bone of short length that serves as a strut between the scapula and the sternum

The clavicle, or collarbone, is a long bone that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right. The clavicle is the only long bone in the body that lies horizontally. Together with the shoulder blade, it makes up the shoulder girdle. It is a touchable bone, and in people who have less fat in this region, the location of the bone is clearly visible, as it creates a bulge in the skin. It receives its name from the Latin clavicula, because the bone rotates along its axis like a key when the shoulder is abducted. The clavicle is the most commonly fractured bone. It can easily be fractured due to impacts to the shoulder from the force of falling on outstretched arms or by a direct hit.

Sacrum Triangular-shaped bone at the bottom of the spine

The sacrum, in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of sacral vertebrae S1–S5 between 18 and 30 years of age.

Thorax frontal part of an animals body, between its head and abdomen

The thorax or chest is a part of the anatomy of humans and various other animals located between the neck and the abdomen. The thorax includes the thoracic cavity and the thoracic wall. It contains organs including the heart, lungs, and thymus gland, as well as muscles and various other internal structures. Many diseases may affect the chest, and one of the most common symptoms is chest pain. The word thorax comes from the Greek θώραξ thorax "breastplate, cuirass, corslet" via Latin: thorax.

Lumbar vertebrae Five vertebrae between the pelvis and the rib cage

The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse process and by the absence of facets on the sides of the body. They are designated L1 to L5, starting at the top. The lumbar vertebrae help support the weight of the body, and permit movement.

Axis (anatomy) second cervical vertebra of the spine; the most distinctive characteristic of this bone is the strong odontoid process known or called as the dens which rises perpendicularly from the upper surface of the body; it forms the pivot upon which the atlas

In anatomy, the second cervical vertebra (C2) of the spine is named the axis or epistropheus.

Cervical vertebrae Vertebrae of the neck

In tetrapods, cervical vertebrae are the vertebrae of the neck, immediately below the skull. Truncal vertebrae lie caudal of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have 7 cervical vertebrae, with the only 3 known exceptions being the manatee with 6, the two-toed sloth with 5–6, and the three-toed sloth with 9.

Thoracic vertebrae vertebrae between the cervical vertebrae and the lumbar vertebrae

In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical and lumbar vertebrae; they increase in size going towards the lumbar vertebrae, with the lower ones being a lot larger than the upper. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. By convention, the human thoracic vertebrae are numbered T1–T12, with the first one (T1) located closest to the skull and the others going down the spine toward the lumbar region.

Erector spinae muscles muscle group in humans

The erector spinae or spinal erectors is a set of muscles that straighten and rotate the back.

Costal cartilage bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax

The costal cartilages are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, providing medial extension.

Costovertebral joints

The costovertebral joints are the joints that connect the ribs to the vertebral column. The articulation of the head of the rib connects the head of the rib to the bodies of the thoracic vertebrae.

A costal facet is a site of connection between a rib and a vertebra. The costal facets are located on the vertebrae that the rib articulates with. They are the superior costal facet, the inferior costal facet, and the transverse costal facet. Rib 1 only articulates with a transverse costal facet. A transverse costal facet is a facet on the transverse process of the vertebrae for articulation with the tubercle on the rib.

Costotransverse joint

The costotransverse joint is the joint formed between the facet of the tubercle of the rib and the adjacent transverse process of a thoracic vertebra. The costotransverse joint is a plane type synovial joint which, under physiological conditions, allows only gliding movement.

A Costotransverse ligament is a short fibrous band that connects a rib with the transverse process of vertebra. They are some of the ligaments that surround the costovertebral joint.

Outline of human anatomy Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

Sternum flat bone in the middle front part of the rib cage

The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Shaped roughly like a necktie, it is one of the largest and longest flat bones of the body. Its three regions are the manubrium, the body, and the xiphoid process. The word "sternum" originates from the Greek στέρνο, meaning "chest".

Vertebral column bony structure found in vertebrates

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs. The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

Vertebra bone in the spinal column

In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of which vary according to the segment of the backbone and the species of vertebrate.


  1. 1 2 Netter, Frank (2014). Atlas of human anatomy (Sixth ed.). Saunders. pp. 183–184. ISBN   9781455704187.
  2. 1 2 Saladin, K. S. (2010). Anatomy and Physiology: The Unity of Form and Function (5th ed.). New York, NY: McGraw-Hill.
  3. 1 2 3 Larsen, William (2001). Human embryology (3rd ed.). Churchill Livingstone. pp. 80–85. ISBN   0443065837.
  4. 1 2 3 4 5 Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 170–173. ISBN   0-03-910284-X.