The rib cage, as an enclosure that comprises the

rib In vertebrate anatomy, ribs ( la, 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 ches ...

vertebral column 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 (a flexible rod of uniform composition) found in all chordata, ...

and

sternum 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. Sh ...

in the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

of most

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s, protects

vital organ In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...

s such as the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s and

great vessels Great vessels are the large vessels that bring blood to and from the heart. These are: *Superior vena cava *Inferior vena cava *Pulmonary arteries *Pulmonary veins *Aorta Transposition of the great vessels is a group of congenital heart defect ...

. The sternum, together known as the thoracic cage, is a semi-rigid bony and

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...

structure which surrounds the

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

and supports the

shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...

to form the core part of the

human skeleton The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton makes up a ...

. A typical human thoracic cage consists of 12 pairs of ribs and the adjoining costal cartilages, the sternum (along with the

manubrium 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. Sha ...

and xiphoid process), and the 12 thoracic vertebrae articulating with the ribs. Together with the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

and associated

fascia A fascia (; plural fasciae or fascias; adjective fascial; from Latin: "band") is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches to, stabilizes, encloses, and separates muscles and other internal organs. ...

and

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s, the thoracic cage makes up the thoracic wall and provides attachments for extrinsic

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

upper limb The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulde ...

s, upper abdomen and back. The rib cage intrinsically holds the muscles of respiration (

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

, intercostal muscles, etc.) that are crucial for active

inhalation Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

and forced exhalation, and therefore has a major ventilatory function in the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

Structure

There are thirty-three vertebrae in the human vertebral column. The rib cage is associated with TH1−TH12. Ribs are described based on their location and connection with the sternum. All ribs are attached posteriorly to the thoracic vertebrae and are numbered accordingly one to twelve. Ribs that articulate directly with the sternum are called ''true ribs'', whereas those that do not articulate directly are termed ''false ribs''. The ''false ribs'' include the ''floating ribs'' (eleven and twelve) that are not attached to the sternum at all.

Attachment

The terms ''true ribs'' and ''false ribs'' describe rib pairs that are directly or indirectly attached to the sternum respectively. The first seven rib pairs known as the ''fixed'' or vertebrosternal ribs are the ''true ribs'' ( la, costae verae) as they connect directly to the sternum; the next five pairs (eighth to twelfth) are the ''false ribs'' ( la, costae spuriae). The false ribs include both vertebrochondral ribs and vertebral ribs. There are three pairs of vertebrochondral ribs (eighth to tenth) that connect indirectly to the sternum via the costal cartilages of the ribs above them. Their elasticity allows rib cage movement for respiratory activity. The phrase ''floating rib'' or vertebral rib ( la, costae fluctuantes) refers to the two lowermost, the eleventh and twelfth rib pairs; so-called because they are attached only to the

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

–and not to the sternum or cartilage of the sternum. These ribs are relatively small and delicate, and include a cartilaginous tip. The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, and

neurovascular bundle A neurovascular bundle is a structure that binds nerves and veins (and in some cases arteries and lymphatics) with connective tissue so that they travel in tandem through the body. Structure There are two types of neurovascular bundles: superficia ...

s containing nerves, arteries, and

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

Parts of rib

Each rib consists of a head, neck, and a shaft. All ribs are attached posteriorly to the thoracic vertebrae. They are numbered to match the vertebrae they attach to – one to twelve, from top (T1) to bottom. The head of the rib is the end part closest to the

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

with which it articulates. It is marked by a kidney-shaped articular surface which is divided by a horizontal crest into two articulating regions. The upper region articulates with the

inferior costal facet The inferior costal facet (or inferior costal fovea) is a site where a rib forms a joint with the inferior aspect of the body of a thoracic vertebra. In the adjacent picture, the arrow points to an inferior costal facet. The facets are named for t ...

on the vertebra above, and the larger region articulates with the

superior costal facet The superior costal facet (or superior costal fovea) is a site where a rib forms a joint with the top of a vertebra. Ribs connect to the thoracic vertebrae at two main points, the inferior and superior costal facets. These connection points are l ...

on the vertebra with the same number. The transverse process of a thoracic vertebra also articulates at the transverse costal facet with the tubercle of the rib of the same number. The crest gives attachment to the intra-articular ligament.http://www.teachmeanatomy.com/osteology-of-the-thorax/ The neck of the rib is the 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 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. Types There are three types of costotransverse ligaments in the ...

; its lower border is rounded. On the posterior surface at the neck, is an eminence—the tubercle that consists of an articular and a non-articular portion. The articular portion is the lower and more medial of the two and presents a small, oval surface for articulation with the transverse costal facet 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. The angle of a

(costal angle) may both refer to the bending part of it, and a prominent line in this area, a little in front of the tubercle. This line is directed downward and laterally; this gives attachment to a tendon of the

iliocostalis muscle Iliocostalis muscle is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial. It lies very deep to the fleshy portion of the serratus posterior muscle. It laterall ...

. At this point, the rib is bent in two directions, and at the same time twisted on its long axis. The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The area between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the longissimus dorsi muscle.

Bones

Ribs and vertebrae

The first rib (the topmost one) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward. File:Sobo 1909 24.png, First rib seen from above File:Gray123.png, Costal groove position on a central rib The ''head'' is small and rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra. The ''neck'' is narrow and rounded. The ''tubercle'', thick and prominent, is placed on the outer border. It bears a small facet for articulation with the transverse costal facet on the transverse process of T1. There is no ''angle'', but at the tubercle, the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the

scalene tubercle The scalene tubercle is a small projection that runs along the medial border of the first rib between two grooves, which travel anteriorly for the subclavian artery and posteriorly for the subclavian vein. It projects outward medially, and is the s ...

, for the attachment of the

anterior scalene The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the anterior scalene, middle scalene, and posterior scalene. They are innervated by the third to the eight cervical spinal nerves (C3-C8). The anterior and m ...

; the ''anterior groove'' transmits the

subclavian vein The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption ...

, the ''posterior ''the

subclavian artery In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplie ...

and the lowest trunk of the brachial plexus. Behind the posterior groove is a rough area for the attachment of the medial scalene. The ''under surface'' is smooth and without a costal groove. The ''outer border'' is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the

serratus anterior The serratus anterior is a muscle that originates on the surface of the 1st to 8th ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula. The serratus anterior acts to pull the scapula fo ...

. The ''inner border'' is concave, thin, and sharp, and marked about its center by the scalene tubercle. The ''anterior extremity'' is larger and thicker than that of any of the other ribs. The second rib is the second uppermost rib in humans or second most frontal in animals that walk on four limbs. In humans, the second rib is defined as a true rib since it connects with the sternum through the intervention of the costal cartilage anteriorly (at the front). Posteriorly, the second rib is connected with the

by the second thoracic vertebra. The second rib is much longer than the

first rib The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi-r ...

, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight and situated close to the tubercle. The body is not twisted so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of the lower part of the first and the whole of the second digitation of the serratus anterior; behind and above this is attached the posterior scalene. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove between the ridge of the internal surface of the rib and the inferior border. It protects the intercostal space containing the

intercostal veins The intercostal veins are a group of veins which drain the area between the ribs ("costae"), called the intercostal space. They can be divided as follows: * Anterior intercostal veins * Posterior intercostal veins ** Posterior intercost vein that ...

intercostal arteries The intercostal arteries are a group of arteries that supply the area between the ribs ("costae"), called the intercostal space. The highest intercostal artery (supreme intercostal artery or superior intercostal artery) is an artery in the human ...

, and

intercostal nerves The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and diffe ...

.Moore, Dalley & Agur. 2009. ''Clinically Oriented Anatomy'', 6th Edition. 90 Pp. Lippincott, Williams & Wilkins, , The ninth rib has a frontal part at the same level as the

first lumbar vertebra 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 pr ...

. This level is called the transpyloric plane, since the pylorus is also at this level.Bålens ytanatomi (surface anatomy). Godfried Roomans, Mats Hjortberg and Anca Dragomir. Institution for Anatomy, Uppsala. 2008. The tenth rib attaches directly to the body of vertebra T10 instead of between vertebrae like the second through ninth ribs. Due to this direct attachment, vertebra T10 has a complete costal facet on its body. Skeleton woman back

The eleventh and twelfth ribs, the floating ribs, have a single

articular facet A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

on the head, which is of rather large size. They have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove, whereas the twelfth does not. The twelfth rib is much shorter than the eleventh rib, and only has a one articular facet.

Sternum

The sternum is a long, flat bone that forms the front of the rib cage. The cartilages of the top seven ribs (the ''true ribs'') join with the sternum at the sternocostal joints. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate. The

transversus thoracis The transversus thoracis muscle (), also known as triangularis sterni, lies internal to the thoracic cage, anteriorly. It is usually a thin plane of muscular and tendinous fibers, however on athletic individuals it can be a thick 'slab of meat', ...

muscle is innervated by one of the

and superiorly attaches at the posterior surface of the lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs.

Development

Expansion of the rib cage in males is caused by the effects of

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

during puberty.Testosterone causes expansion of rib cage during puberty as one of secondary sex characteristics. Thus, males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen. C7ribMark

Variation

Variations in the number of ribs occur. About 1 in 200–500 people have an additional

cervical rib A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of the ...

, and there is a female predominance. Intrathoracic supernumerary ribs are extremely rare. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a

, which can mechanically interfere with the nerves ( brachial plexus) going to the arm. In several ethnic groups, most significantly the Japanese, the tenth rib is sometimes a

floating rib The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi-r ...

, as it lacks a cartilaginous connection to the seventh rib.

Function

The human rib cage is a component of the human

. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular

, at the floor of the thoracic cavity, contracts and flattens, while the contraction of intercostal muscles lift the rib cage up and out. Expansion of the thoracic cavity is driven in three planes; the vertical, the anteroposterior and the transverse. The vertical plane is extended by the help of the diaphragm contracting and the abdominal muscles relaxing to accommodate the downward pressure that is supplied to the abdominal viscera by the diaphragm contracting. A greater extension can be achieved by the diaphragm itself moving down, rather than simply the domes flattening. The second plane is the anteroposterior and this is expanded by a movement known as the ' pump handle'. The downward sloping nature of the upper ribs are as such because they enable this to occur. When the external intercostal muscles contract and lift the ribs, the upper ribs are able also to push the sternum up and out. This movement increases the anteroposterior diameter of the thoracic cavity, and hence aids breathing further. The third, transverse, plane is primarily expanded by the lower ribs (some say it is the 7th to 10th ribs in particular), with the diaphragm's central tendon acting as a fixed point. When the diaphragm contracts, the ribs are able to evert (meaning turn outwards or inside out) and produce what is known as the

bucket handle movement Bucket-handle is a movement of ribs that results in change in transverse diameter of the thorax. Definition One of the most important functions of ribs and diaphragm is the change in volume of thorax that helps inspiration and expiration. In g ...

, facilitated by gliding at the

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. Structure The costotransverse joint connects th ...

. In this way, the transverse diameter is expanded and the lungs can fill. The circumference of the normal adult human rib cage expands by 3 to 5 cm during inhalation.

Clinical significance

Rib fracture A rib fracture is a break in a rib bone. This typically results in chest pain that is worse with inspiration. Bruising may occur at the site of the break. When several ribs are broken in several places a flail chest results. Potential complicatio ...

s are the most common injury to the rib cage. These most frequently affect the middle ribs. When several adjacent ribs incur two or more fractures each, this can result in a

flail chest Flail chest is a life-threatening medical condition that occurs when a segment of the rib cage breaks due to trauma and becomes detached from the rest of the chest wall. Two of the symptoms of flail chest are chest pain and shortness of breath. ...

which is a life-threatening condition. A dislocated rib can be painful and can be caused simply by coughing, or for example by trauma or lifting heavy weights. One or more costal cartilages can become inflamed – a condition known as costochondritis; the resulting pain is similar to that of a heart attack. Abnormalities of the rib cage include pectus excavatum ("sunken chest") and

pectus carinatum Pectus carinatum, also called pigeon chest, is a malformation of the chest characterized by a protrusion of the sternum and ribs. It is distinct from the related malformation pectus excavatum. Signs and symptoms People with pectus carinatum usua ...

("pigeon chest"). A

bifid rib A bifid rib is a congenital abnormality of the rib cage and associated muscles and nerves which occurs in about 1.2% of humans. Bifid ribs occur in up to 8.4% of Samoans. The sternal end of the rib is cleaved into two. It is usually unilateral. ...

is a bifurcated rib, split towards the sternal end, and usually just affecting one of the ribs of a pair. It is a

congenital defect A birth defect, also known as a congenital disorder, is an abnormal condition that is present at childbirth, birth regardless of its cause. Birth defects may result in disability, disabilities that may be physical disability, physical, intellect ...

affecting about 1.2% of the population. It is often without symptoms though respiratory difficulties and other problems can arise.

Rib removal Rib removal is surgery to remove one or more ribs. Rib resection is the removal of part of a rib. The procedures are done for various medical reasons. A number of celebrities have been falsely rumoured to have had ribs removed as a form of body mod ...

is the surgical removal of one or more ribs for therapeutic or cosmetic reasons. Rib resection is the removal of part of a rib.

Regeneration

Since the early part of the 20th century, the ability of the human rib to regenerate itself has been appreciated. However, scientific reports demonstrating repair have been sporadic and anecdotal. Currently, this phenomenon is best taken advantage of by craniomaxillofacial surgeons, who use both cartilage and bone material from the rib for jaw, face, and ear reconstruction. The perichondrium is a fibrous sheath of vascular connective tissue surrounding the rib cartilage, containing a source of progenitor stem cells required for rib regeneration.

Society and culture

The position of ribs can be permanently altered by a form of body modification called

tightlacing Tightlacing (also called corset training) is the practice of wearing a tightly-laced corset. It is done to achieve cosmetic modifications to the figure and posture or to experience the sensation of bodily restriction. History Corsets were first ...

, which uses a

corset A corset is a support garment commonly worn to hold and train the torso into a desired shape, traditionally a smaller waist or larger bottom, for aesthetic or medical purposes (either for the duration of wearing it or with a more lasting effe ...

to compress and move the ribs. The ribs, particularly their sternal ends, are used as a way of estimating age in forensic pathology due to their progressive ossification.

Biblical Story

The number of ribs as 24 (12 pairs) was noted by the

Flemish Flemish (''Vlaams'') is a Low Franconian dialect cluster of the Dutch language. It is sometimes referred to as Flemish Dutch (), Belgian Dutch ( ), or Southern Dutch (). Flemish is native to Flanders, a historical region in northern Belgium; ...

anatomist Vesalius in his key work of anatomy ''

De humani corporis fabrica ''De Humani Corporis Fabrica Libri Septem'' (Latin, lit. "On the fabric of the human body in seven books") is a set of books on human anatomy written by Andreas Vesalius (1514–1564) and published in 1543. It was a major advance in the history ...

'' in 1543, setting off a wave of controversy, as it was traditionally assumed from the Biblical story of Adam and Eve that men's ribs would number one fewer than women's. This false belief is still commonly believed today. However, thirteenth or “cervical rib” occurs in 1% of humans and this is more common in females than in males.

Other animals

herpetology Herpetology (from Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and rept ...

, costal grooves refer to lateral indents along the integument of

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

s. The grooves run between the axilla to the groin. Each groove overlies the myotomal septa to mark the position of the internal rib.J. W. Petranka. 1998. Salamanders of the United States and Canada. 587 Pp. Smithsonian Institution Press, ,

Birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

and

reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...

have bony uncinate processes on their ribs that project caudally from the vertical section of each rib. These serve to attach

sacral Sacral may refer to: *Sacred, associated with divinity and considered worthy of spiritual respect or devotion *Of the sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spi ...

muscles and also aid in allowing greater inspiration.

Crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s have cartilaginous uncinate processes.

Additional images

File:Thoracic Cage with Spine - Anatomy.gif, Thoracic cage with spine File:Gray115.png, Anterior surface of sternum and costal cartilages File:Ribs labeled.png, X-ray image of a human chest, with ribs labelled File:BodyParts3D Rib cage.stl, 3D model of rib cage File:Surface projections of the organs of the trunk.png, Surface projections of the trunk, including each rib, and the costal margin File:Thoracic Cage with Both Humerii.gif, Thoracic cage with both humerii

Notes

References

* ''Orientation of the intercostal muscle fibers in the human rib cage'', Subit D., Glacet A., Hamzah M., Crandall J., Computer Methods in Biomechanics and Biomedical Engineering, 2015, 18, pp. 2064–2065 * ''Clinically Oriented Anatomy'', 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64 * ''Principles of Anatomy Physiology'', Tortora GJ and Derrickson B. 11th ED. John Wiley and Sons, 2006. *
De Humani Corporis Fabrica
': online English translation of Vesalius' books on human anatomy.

External links

{{DEFAULTSORT:Rib cage Bones of the thorax