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55-454: Traditionally, Carinatae were defined as all birds whose sternum (breast bone) has a keel ( carina ). The keel is a strong median ridge running down the length of the sternum. This is an important area for the attachment of flight muscles. Thus, all flying birds have a pronounced keel. Ratites , all of which are flightless, lack a strong keel. Thus, living birds were divided into carinatae (keeled) and ratites (from ratis , "raft", referring to

110-443: A cervical rib . People may have a cervical rib on the right, left or both sides. All are attached at the back to the thoracic vertebrae and are numbered from 1 to 12 according to the vertebrae to which they attach. The first rib is attached to thoracic vertebra 1 (T1). At the front of the body, most of the ribs are joined by costal cartilage to the sternum . Ribs connect to vertebrae at the costovertebral joints . The parts of

165-423: A corresponding one on the xiphoid process, forms a notch for the cartilage of the seventh rib. These articular depressions are separated by a series of curved interarticular intervals, which diminish in length from above downward, and correspond to the intercostal spaces. Most of the cartilages belonging to the true ribs , articulate with the sternum at the lines of junction of its primitive component segments. This

220-432: A front and back surface. It is flat on the front, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth articular depressions. The pectoralis major attaches to it on either side. At the junction of the third and fourth parts of the body is occasionally seen an orifice, the sternal foramen, of varying size and form. The posterior surface, slightly concave,

275-418: A high BMI (obese or grossly overweight) may present with excess tissue that makes access to traditional marrow biopsy sites such as the pelvis difficult. A somewhat rare congenital disorder of the sternum sometimes referred to as an anatomical variation is a sternal foramen, a single round hole in the sternum that is present from birth and usually is off-centered to the right or left, commonly forming in

330-402: A keeled breastbone is Confuciusornis . While some specimens of this stem-bird have flat breastbones, some show a small ridge that could have supported a cartilaginous keel. This bird-related article is a stub . You can help Misplaced Pages by expanding it . Sternum The sternum ( pl. : sternums or sterna ) or breastbone is a long flat bone located in the central part of

385-432: A radical surgery, usually to surgically treat a malignancy, either with or without a mediastinal lymphadenectomy ( Current Procedural Terminology codes # 21632 and # 21630, respectively). A bifid sternum is an extremely rare congenital abnormality caused by the fusion failure of the sternum. This condition results in sternal cleft which can be observed at birth without any symptom. The sternum, in vertebrate anatomy,

440-443: A rib includes 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. The crest gives attachment to

495-459: A single set of ribs which are probably homologous with the dorsal ribs of fishes. In the earlier choanates , 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 . In most true tetrapods, many of these early ribs have been lost, and in living amphibians and reptiles , there

550-480: Is a flat bone that lies in the middle front part of the rib cage . It is endochondral in origin. It probably first evolved in early tetrapods as an extension of the pectoral girdle ; it is not found in fish . In amphibians and reptiles , it is typically a shield-shaped structure, often composed entirely of cartilage . It is absent in both turtles and snakes . In birds , it is a relatively large bone and typically bears an enormous projecting keel to which

605-437: Is a narrow, flat bone , forming the middle portion of the front of the chest . The top of the sternum supports the clavicles (collarbones) and its edges join with the costal cartilages of the first two pairs of ribs . The inner surface of the sternum is also the attachment of the sternopericardial ligaments . Its top is also connected to the sternocleidomastoid muscle . The sternum consists of three main parts, listed from

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660-457: 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 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, and attaches to the manubrium. The vertebral attachment can be found just below

715-469: Is actually more like the Latin os pectoris , derived from classical Latin os , bone and pectus , chest or breast. Confusingly, pectus is also used in classical Latin as breastbone . Rib 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 thoracic cavity , enabling

770-432: Is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the transversus thoracis takes origin. The sternal angle is located at the point where the body joins the manubrium. The sternal angle can be felt at the point where the sternum projects farthest forward. However, in some people the sternal angle is concave or rounded. During physical examinations,

825-400: 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. In birds, ribs are present as distinct bones only on

880-442: Is rare and usually caused by severe trauma. It may also result from minor trauma where there is a precondition of arthritis. The breastbone is sometimes cut open (a median sternotomy ) to gain access to the thoracic contents when performing cardiothoracic surgery . Surgical fixation of sternotomy is achieved through the use of either wire cerclage or a plate and screw technique. The incidence of sternotomy complications falls within

935-424: Is well seen in some other vertebrates, where the parts of the bone remain separated for longer. The upper border is oval and articulates with the manubrium, at the sternal angle. The lower border is narrow, and articulates with the xiphoid process . Located at the inferior end of the sternum, is the pointed xiphoid process . Improperly performed chest compressions during cardiopulmonary resuscitation can cause

990-439: 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 Ancient Greek στέρνον ( stérnon ) 'chest'. The sternum

1045-426: The chest of both sexes . The Greek physician Hippocrates used στέρνον to refer to the chest , and στῆθος to the breastbone . The Greek physician Galen was the first to use στέρνον in the present meaning of breastbone . The sternum as the solid bony part of the chest can be related to Ancient Greek στερεός/στερρός , ( stereόs/sterrόs ) , meaning firm or solid . The English term breastbone

1100-404: 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 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

1155-424: 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 then become longer and less curved as they progress downwards. 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

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1210-426: 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 ventral ribs, and only very short dorsal ribs. In some teleosts , there may be additional rib-like bones within the muscle mass. Tetrapods , however, only ever have

1265-446: 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. The rib cage is separated from the lower abdomen by the thoracic diaphragm which controls breathing. When

1320-436: The 1980s, Carinatae was given several phylogenetic definitions. The first was as a node-based clade uniting Ichthyornis with modern birds. However, in many analyses, this definition would be synonymous with the more widely used name Ornithurae . An alternate definition was provided in 2001, naming Carinatae an apomorphy -based clade defined by the presence of a keeled sternum. The most primitive known bird relative with

1375-416: The 2nd, 3rd, and 4th segments of the breastbone body. Congenital sternal foramina can often be mistaken for bullet holes. They are usually without symptoms but can be problematic if acupuncture in the area is intended. Fractures of the sternum are rather uncommon. They may result from trauma, such as when a driver's chest is forced into the steering column of a car in a car accident . A fracture of

1430-400: The body of the sternum, the clavicles and the cartilages of the first 1.5 pairs of ribs . The inferior border, oval and rough, is covered with a thin layer of cartilage for articulation with the body. The lateral borders are each marked above by a depression for the first costal cartilage , and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for

1485-406: The bony tissue is generally only superficial, the central portion of the intervening cartilage remaining unossified. The body of the sternum is formed by the fusion of four segments called sternebrae . In 2.5–13.5% of the population, a foramen known as sternal foramen may be presented at the lower third of the sternal body. In extremely rare cases, multiple foramina may be observed. Fusion of

1540-440: 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. 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

1595-399: 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

1650-405: The first year after birth; and in the xiphoid process, between the fifth and eighteenth years. The centers make their appearance at the upper parts of the segments, and proceed gradually downward. To these may be added the occasional existence of two small episternal centers, which make their appearance one on either side of the jugular notch ; they are probably vestiges of the episternal bone of

1705-479: The flatness of the sternum). The difficulty with this scheme phylogenetically was that some flightless birds, without strong keels, are descended directly from ordinary flying birds possessing one. Examples include the kākāpō , a flightless parrot , and the dodo , a columbiform (the pigeon family). Neither of these birds are a ratite. Thus, this supposedly distinctive feature was easy to use, but had nothing to do with actual phylogenetic relationship. Beginning in

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1760-428: The flight muscles are attached. Only in mammals does the sternum take on the elongated, segmented form seen in humans. In arthropods, a sternum is the ventral part of a segment of thorax or abdomen . English sternum is a translation of Ancient Greek στέρνον , sternon . The Greek writer Homer used the term στέρνον to refer to the male chest , and the term στῆθος , stithos to refer to

1815-403: The head and neck. During adolescence secondary ossification centers are formed in the tubercles and heads of the ribs. In jawed 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,

1870-418: 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

1925-414: The irregular union of which explains the rare occurrence of the sternal foramen [Fig. 7], or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as fissura sterni; these conditions are further explained by the manner in which the cartilaginous sternum is formed. More rarely still the upper end of the sternum may be divided by a fissure . Union of

1980-406: The lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs. The sternum develops from two cartilaginous bars one on the left and one on the right, connected with the cartilages of the ribs on each side. These two bars fuse together along the middle to form the cartilaginous sternum which is ossified from six centers: one for

2035-450: The lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs , heart , and other vital organs of the thorax. In some animals, especially snakes , ribs may provide support and protection for the entire body. Human ribs are flat bones that form part of the rib cage to help protect internal organs. Humans usually have 24 ribs, in 12 pairs. 1 in 500 people have an extra rib known as

2090-458: The male than in the female. The manubrium ( Latin for 'handle') is the broad upper part of the sternum. It has a quadrangular shape, narrowing from the top, which gives it four borders. The suprasternal notch (jugular notch) is located in the middle at the upper broadest part of the manubrium. This notch can be felt between the two clavicles . On either side of this notch are the right and left clavicular notches . The manubrium joins with

2145-428: The manubriosternal joint also occurs in around 5% of the population. Small ossicles known as episternal ossicles may also be present posterior to the superior end of the manubrium. Another variant called suprasternal tubercle is formed when the episternal ossicles fuse with the manubrium. Because the sternum contains bone marrow , it is sometimes used as a site for bone marrow biopsy . In particular, patients with

2200-404: The manubrium, four for the body, and one for the xiphoid process . The ossification centers appear in the intervals between the articular depressions for the costal cartilages , in the following order: in the manubrium and first piece of the body, during the sixth month of fetal life; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during

2255-447: The monotremata and lizards. Occasionally some of the segments are formed from more than one center, the number and position of which vary [Fig. 6]. Thus, the first piece may have two, three, or even six centers. When two are present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally,

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2310-443: The narrow range of 0.5% to 5%. Nevertheless, these complications can have severe consequences, including increased mortality rates, the need for reoperation, and a mortality rate as high as 40%. Such complications often entail issues like dehiscence and sternal non-union, primarily stemming from lateral forces exerted during post-operative activities such as coughing and sneezing. The sternum can be totally removed (resected) as part of

2365-429: 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. 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

2420-430: The reception of the costal cartilage of the second rib. Between the depression for the first costal cartilage and the demi-facet for the second is a narrow, curved edge, which slopes from above downward towards the middle. Also, the superior sternopericardial ligament attaches the pericardium to the posterior side of the manubrium. The body, or gladiolus, is the longest sternal part. It is flat and considered to have only

2475-426: 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

2530-399: 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. 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

2585-414: The sclerotomes. 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

2640-401: The sternal angle is a useful landmark because the second rib attaches here. Each outer border, at its superior angle, has a small facet, which with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib; below this are four angular depressions which receive the cartilages of the third, fourth, fifth, and sixth ribs. The inferior angle has a small facet, which, with

2695-516: The sternum is usually a comminuted fracture. The most common site of sternal fractures is at the sternal angle . Some studies reveal that repeated punches or continual beatings, sometimes called "breastbone punches", to the sternum area have also caused fractured sternums. Those are known to have occurred in contact sports such as hockey and football. Sternal fractures are frequently associated with underlying injuries such as pulmonary contusions , or bruised lung tissue. A manubriosternal dislocation

2750-425: 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

2805-406: 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. 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 therian mammals,

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2860-422: The top five ribs join with the sternum at the sternocostal joints . The right and left clavicular notches articulate with the right and left clavicles, respectively. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate. The transversus thoracis muscle is innervated by one of the intercostal nerves and superiorly attaches at the posterior surface of

2915-415: The top: In its natural position, the sternum is angled obliquely, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. In adults the sternum is on average about 1.7 cm longer in

2970-425: The various centers of the body begins about puberty , and proceeds from below upward [Fig. 5]; by the age of 25 they are all united. The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however,

3025-400: The xiphoid process to snap off, driving it into the liver which can cause a fatal hemorrhage. The sternum is composed of highly vascular tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles . The inferior sternopericardial ligament attaches the pericardium to the posterior xiphoid process. The cartilages of

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