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

The human rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic (chest) cavity and supports the pectoral (shoulder) girdle, forming a core portion of the human skeleton. A typical human rib cage consists of 24 ribs, the sternum, costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, makes up the thoracic wall, and provides attachments for the muscles of the neck, thorax, upper abdomen, and back.

The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out. These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air.

Contents 1 Rib anatomy 1.1 Atypical ribs 1.2 Number of ribs 2 Medical issues 3 Additional images 4 See also 5 References 6 External links

[edit] Rib anatomy

All ribs are attached in the back to the thoracic vertebrae.

The upper seven true ribs (costae verae, vertebrosternal ribs, I-VII). are attached in the front to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.

The 8th, 9th, and 10th ribs are called false ribs (costae spuriae, vertebrochondral ribs, VIII-X), and join with the costal cartilages of the ribs above.

The 11th and 12th ribs are known as floating ribs (costae fluitantes, vertebral ribs, XI-XII), as they do not have any anterior connection to the sternum.

The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries.

The human rib parts:

• The head is the end of a rib closest to the vertebral column.
• The Costovertebral joints are the articulations that connect the heads of the ribs to the thoracic vertebrae.
• The neck is the flattened portion which extends lateralward from the head.
• The tubercle is an eminence on the posterior surface.
• The angle is a bending part.
• The Costal groove is a groove between the ridge of the internal surface of the rib and the inferior border.

[edit] Atypical ribs

The atypical ribs are the 1st, 2nd, and 11th and 12th.

• The first rib is a shaft that is wide and nearly horizontal and has the sharpest curve of the seven true ribs. Its head has a single facet to articulate with the first thoracic vertebra (T1). It also has two grooves for the subclavian vessels, which are separated by the scalene tubercle.

• The second rib is thinner, less curved, and longer than the first rib. It has two facets to articulate with T2 and T1, and a tubercle for muscles to attach to.

• The 11th and 12th ribs have only one facet on their head; the 11th and 12th ribs are short with no necks or tubercles and terminate in the abdominal wall before fusing with the costal cartilages.

[edit] Number of ribs

The number of ribs was noted by the Flemish anatomist Vesalius in his key work of anatomy De humani corporis fabrica 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.^[1] Variations in the number of ribs occur. About 1 in 200 people has an additional cervical rib and there is a female predominance.^[2] Intrathoracic supernumerary ribs are extremely rare.^[3]

[edit] Medical issues

Rib fractures are the most common injury to the rib cage. These most frequently affect the middle ribs. When several ribs are injured, this can result in a flail chest.

Abnormalities of the rib cage include pectus excavatum ("sunken chest") and pectus carinatum ("pigeon chest"). Bifid or bifurcated ribs, in which the sternal end of the rib is cleaved in two, is a congenital abnormality occurring in about 1.2% of the population. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a cervical rib, which can cause problems in the nerves going to the arm.

Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.

[edit] Additional images

Anterior surface of sternum and costal cartilages.
		X-ray image of human chest, with ribs labeled.	Thoracic cage.
Side view of human rib cage. Seen are the 5-12 spareribs under lean muscle.

[edit] See also

• Terms for bones
• Terms for anatomical location
• Articulation of head of rib

[edit] References

1. ^ "Chapter 19 On the Bones of the Thorax". http://vesalius.northwestern.edu/ixmlquery/hilight?parm1=chapters/FA.1.19&keyword=rib&scrollpoint=FA.1.19.07&. Retrieved 2007-08-23. 
2. ^ Kurihara Y; Yakushiji YK, Matsumoto J, Ishikawa T, Hirata K (Jan-Feb 1999). "The Ribs: Anatomic and Radiologic Considerations" (PDF). RadioGraphics (Radiological Society of North America) 19 (1): 105–119. ISSN 1527-1323. PMID 9925395. http://radiographics.rsna.org/content/19/1/105.full.pdf. Retrieved August 13, 2009. 
3. ^ Kamano H; Ishihama T, Ishihama H, Kubota Y, Tanaka T, Satoh K (June 1, 2006). "Bifid intrathoracic rib: a case report and classification of intrathoracic ribs" (PDF). Internal Medicine (The Japanese Society of Internal Medicine) 45 (9): 627-630. doi:10.2169/internalmedicine.45.1502. PMID 16755094. http://www.jstage.jst.go.jp/article/internalmedicine/45/9/627/_pdf. Retrieved August 13, 2009. 

• 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. ISBN 0-471-68934-3
• De Humani Corporis Fabrica: online English translation of Vesalius' books on human anatomy.

[edit] External links

• Anatomy at MUN thorax/cage
• Diagram at mhhe.com

v • d • e Bones of torso (TA A02.2,3, GA 2.96-128) Sternum Suprasternal notch, Manubrium, Sternal angle, Body of sternum, Xiphisternal joint, Xiphoid process Rib specific ribs (1, 2, 9, 10, 11, 12, true – 1–7, false – 8–12, floating – 11–12) · parts (Angle, Tubercle, Costal groove, Neck, Head) Superior thoracic aperture · Inferior thoracic aperture · Intercostal space · Thoracic wall/Thoracic cage Vertebra General structures body of vertebra, vertebral arch (pedicle, lamina, vertebral notch), foramina (vertebral, intervertebral), processes (transverse, articular/zygapophysis, spinous), spinal canal Cervical vertebrae C1 (anterior arch, posterior arch, lateral mass), C2 (dens), C3, C4, C5, C6, C7 anterior tubercle, posterior tubercle, foramen transversarium Thoracic vertebrae T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12 costal facets (superior, inferior, transverse) Lumbar vertebrae accessory process, mammillary process, L5 Sacrum pelvic surface (anterior sacral foramina), dorsal surface (posterior sacral foramina, median sacral crest, medial sacral crest, lateral sacral crest), lateral surface (sacral tuberosity), base, sacral hiatus · presacral space · sacral promontory · sacral canal  · ala of sacrum · sacrovertebral angle Coccyx

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