Editing Rib cage (section)

==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 vertebra]]e 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 [[human sternum|sternum]] respectively. The first seven rib pairs known as the ''fixed'' or ''vertebrosternal'' ribs are the ''true ribs'' ({{langx|la|costae verae}}) as they connect directly to the sternum via their own individual [[costal cartilage]]s. The next five pairs (eighth to twelfth) are the ''false ribs'' ({{langx|la|costae spuriae}}) or ''vertebrochondral'' ribs, which do not connect directly to the sternum.  The first three pairs of vertebrochondral ribs (eighth to tenth) connect indirectly to the sternum via the costal cartilages of the ribs above them,<ref name=":0">{{cite web|title=The Thoracic Cage · Anatomy and Physiology|url=http://philschatz.com/anatomy-book/contents/m46350.html|access-date=10 March 2018|language=en-us}}</ref><ref name=":1">{{cite book|last1=Hyman|first1=Libbie Henrietta|title=Hyman's Comparative Vertebrate Anatomy |date=1992 |publisher=University of Chicago Press |isbn=9780226870137 |page=230 |url=https://books.google.com/books?id=VKlWjdOkiMwC|access-date=10 March 2018|language=en}}</ref> and the overall elasticity of their articulations allows the [[bucket handle movement]]s of the rib cage essential for respiratory activity.

The phrase ''floating rib'' ({{langx|la|costae fluctuantes}}) or ''vertebral'' rib refers to the two lowermost (the eleventh and twelfth) rib pairs; so-called because they are attached only to the [[vertebrae]] and not to the sternum or any of the costal cartilages. These ribs are relatively small and delicate, and include a cartilaginous tip.<ref name="saladin">{{Cite book   | last1 = Saladin | first1 = Kenneth   | title = Anatomy and Physiology: The Unity of Form and Function   | location = USA   | publisher = [[The McGraw-Hill Companies, Inc.]]   | year= 2010   | pages = 485   | isbn = 978-0-07-352569-3 }}</ref>

The spaces between the ribs are known as [[intercostal space]]s; they contain the instrinsic [[intercostal muscle]]s and the [[neurovascular bundle]]s containing [[intercostal nerve]]s, [[intercostal arteries|arteries]] and [[Intercostal veins|veins]].<ref name="Smith">{{cite web |last1=Smith |first1=Sarah |title=Intercostal spaces {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/intercostal-spaces |website=radiopaedia.org |language=en}}</ref> The superficial surface of the rib cage is covered by the [[thoracolumbar fascia]], which provides external attachments for the [[neck muscles|neck]], [[back muscles|back]], [[pectoral muscles|pectoral]] and [[abdominal muscle]]s.

<gallery mode="packed" heights="200px">
File:vrParaPersp.gif|Human rib cage - CT scan (parallel projection (left) and perspective projection (right))
File:Costillas.png|{{legend|red|true / fixed ribs}} {{legend|#00ff00|false ribs}}{{legend|blue|false and floating ribs}}|alt=true / fixed ribs   false ribs  false and floating ribs
</gallery>

===Parts of rib===
[[Image:Gray122.png|thumb|The parts of the 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]] with which it [[Articulation of head of rib|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]] on the vertebra above, and the larger region articulates with the [[superior costal facet]] 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 of head of rib|intra-articular ligament]].<ref name=":2">{{Cite web |date=2013-05-02 |title=Osteology of the Thorax |website=TeachMeAnatomy |url=http://teachmeanatomy.info/osteology-of-the-thorax/ |access-date=2024-05-28 |archive-date=2013-05-02 |archive-url=https://web.archive.org/web/20130502062608/http://teachmeanatomy.info/osteology-of-the-thorax/ |url-status=dead}}</ref>

The neck of the rib is the flattened part that extends laterally from the head. The neck is about 3&nbsp;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.

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 [[rib]] (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]]. 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|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.

<gallery widths="250">
File:Sobo 1909 24.png|First rib seen from above
File:Gray123.png|Costal groove position on a central rib
</gallery>

The ''head'' is small and rounded, and possesses only a single articular facet, for articulation with the body of the first [[Thoracic vertebrae|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]], for the attachment of the [[scalene muscles|anterior scalene]]; the ''anterior groove'' transmits the [[subclavian vein]], the ''posterior ''the [[subclavian artery]] and the lowest trunk of the [[brachial plexus]]. Behind the posterior groove is a rough area for the attachment of the [[scalene muscles|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 ''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 [[vertebral column]] by the [[Thoracic vertebrae#Second thoracic vertebra|second thoracic vertebra]]. The second rib is much longer than the [[first rib]], 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 [[scalene muscles|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]], [[intercostal arteries]], and [[intercostal nerves]].<ref name=":3">Moore, Dalley & Agur. 2009. ''Clinically Oriented Anatomy'', 6th Edition. 90 Pp. Lippincott, Williams & Wilkins, {{ISBN|0-7817-7525-6}}, {{ISBN|978-0-7817-7525-0}}</ref><ref name="Smith"/>

The '''ninth rib''' has a frontal part at the same level as the [[first lumbar vertebra]]. This level is called the [[transpyloric plane]], since the [[pylorus]] is also at this level.<ref name=goodfried>Bålens ytanatomi (surface anatomy). Godfried Roomans, Mats Hjortberg and Anca Dragomir. Institution for Anatomy, Uppsala. 2008.</ref>

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.<ref name="saladin"/>

[[File:Skeleton woman back.png|thumb|right|upright=0.6|The four floating ribs indicated]]

The '''eleventh and twelfth ribs''', the '''floating ribs''', have a single [[articular facet]] 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.<ref name=":4">{{Cite journal |last1=Jung |first1=Jaewoong |last2=Lee |first2=Misoon |last3=Choi |first3=Dasom |date=2020-09-04 |title=Twelfth rib syndrome: a case report |journal=The Journal of International Medical Research |volume=48 |issue=9 |pages=0300060520952651 |doi=10.1177/0300060520952651 |issn=0300-0605 |pmc=7479855 |pmid=32883133}}</ref>

====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.<ref name=SA>{{cite book |author=Agur, Anne M.R. |author2= Dalley, Arthur F. II |year=2009 |title= Grant's Atlas of Anatomy, Twelfth Edition |url=https://archive.org/details/grantsatlasanato00agur_396 |url-access=limited |publisher=Lippincott Williams and Wilkins |location=Philadelphia, PA |page= [https://archive.org/details/grantsatlasanato00agur_396/page/n44 10] |isbn= 978-0-7817-7055-2}}</ref>

The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of the [[sternoclavicular joint]], between the sternum and clavicle. The first ribs also attach to the manubrium.<ref name="Openstax Anatomy & Physiology attribution">{{CC-notice|cc=by4|url=https://openstax.org/books/anatomy-and-physiology/pages/7-4-the-thoracic-cage}} {{cite book|last1=Betts|first1=J Gordon |last2=Desaix |first2=Peter |last3=Johnson |first3=Eddie |last4=Johnson |first4=Jody E |last5=Korol |first5=Oksana |last6=Kruse |first6=Dean |last7=Poe |first7=Brandon |last8=Wise |first8=James |last9=Womble|first9=Mark D|last10=Young|first10=Kelly A|title=Anatomy & Physiology |location=Houston |publisher=OpenStax CNX|isbn=978-1-947172-04-3|date=May 14, 2023|at=7.4 The Thoracic Cage}}</ref>

The [[transversus thoracis]] muscle is innervated by one of the [[intercostal nerves]] 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.<ref name=SB>{{cite book |author=Agur, Anne M.R. |author2= Dalley, Arthur F. II |year=2009 |title= Grant's Atlas of Anatomy, Twelfth Edition |url=https://archive.org/details/grantsatlasanato00agur_396 |url-access=limited |publisher=Lippincott Williams and Wilkins |location=Philadelphia, PA |page= [https://archive.org/details/grantsatlasanato00agur_396/page/n65 21] |isbn= 978-0-7817-7055-2}}</ref>

===Development===
Expansion of the rib cage in males is caused by the effects of [[testosterone]] during puberty.<ref name=":5">Testosterone causes expansion of rib cage during puberty as one of secondary sex characteristics.{{cite web |url=http://www.humanhormones.com/category/steroids/androgens/ |title=Archived copy |access-date=2013-12-31 |url-status=dead |archive-url=https://web.archive.org/web/20150911093949/http://www.humanhormones.com/category/steroids/androgens/ |archive-date=2015-09-11 }}</ref> Thus, males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen.

The development of the rib cage is influenced by a combination of genetic and environmental factors, as well as specific stages of embryonic growth. '''Genetic factors''' play a critical role, with specific genes regulating the formation of bones and cartilage to ensure the proper development and alignment of the ribs and sternum. During the '''embryonic stage''', the rib cage begins to form from the mesoderm, one of the three primary germ layers. Ribs develop from structures called somites, which later segment into vertebrae and ribs. Initially, the ribs are composed of '''cartilage''', which gradually ossifies into bone through a process known as endochondral ossification.

As the embryo grows, the ribs elongate and differentiate into three types: '''true ribs''', which attach directly to the sternum; '''false ribs''', which connect to the sternum via cartilage; and '''floating ribs''', which do not attach to the sternum. Additionally, '''environmental factors''' such as maternal health, nutrition, and exposure to certain substances can impact rib cage development. For instance, deficiencies in essential nutrients like calcium and vitamin D may hinder proper bone growth and development. Together, these genetic, developmental, and environmental influences ensure the formation of a functional rib cage.[[File:C7ribMark.png|thumb|150 px|right|A C7 rib on the right]]

===Variation===
Variations in the number of ribs occur. About 1 in 200–500 people have an additional [[cervical rib]], and there is a female predominance.<ref name=":6">{{cite journal | author = Kurihara Y |author2=Yakushiji YK |author3=Matsumoto J |author4=Ishikawa T |author5=Hirata K  |date=Jan–Feb 1999 | title = The Ribs: Anatomic and Radiologic Considerations | journal = RadioGraphics | volume = 19 | issue = 1 | pages = 105–119 | publisher   = Radiological Society of North America | issn = 1527-1323 | pmid = 9925395 | url = http://radiographics.rsna.org/content/19/1/105.full.pdf | access-date = August 13, 2009 | doi=10.1148/radiographics.19.1.g99ja02105| doi-access = free }}</ref> Intrathoracic supernumerary ribs are extremely rare.<ref name=":7">{{cite journal | author = Kamano H | author2 = Ishihama T | author3 = Ishihama H | author4 = Kubota Y | author5 = Tanaka T | author6 = Satoh K | date = June 1, 2006 | title = Bifid intrathoracic rib: a case report and classification of intrathoracic ribs | journal = Internal Medicine | volume = 45 | issue = 9 | pages = 627–630 | publisher = The Japanese Society of Internal Medicine | pmid = 16755094 | doi = 10.2169/internalmedicine.45.1502 | doi-access = free }}</ref> The rib remnant of the [[Vertebra prominens|7th cervical vertebra]] on one or both sides is occasionally replaced by a free extra rib called a [[cervical rib]], 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]], as it lacks a cartilaginous connection to the seventh rib.<ref name="saladin"/>