vertebrates 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, ...

, thoracic vertebrae compose the middle segment of the

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, ...

, between the

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

and the

lumbar vertebrae 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 p ...

. In humans, there are twelve thoracic

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 characteristi ...

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 much larger than the upper. They are distinguished by the presence of

facets A facet is a flat surface of a geometric shape, e.g., of a cut gemstone. Facet may also refer to: Arts, entertainment, and media * ''Facets'' (album), an album by Jim Croce * ''Facets'', a 1980 album by jazz pianist Monty Alexander and his tri ...

on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the

transverse process 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 ...

es 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.

General characteristics

These are the general characteristics of the second through eighth thoracic vertebrae. The first and ninth through twelfth vertebrae contain certain peculiarities, and are detailed below. The

bodies Bodies may refer to: * The plural of body * ''Bodies'' (2004 TV series), BBC television programme * Bodies (upcoming TV series), an upcoming British crime thriller limited series * "Bodies" (''Law & Order''), 2003 episode of ''Law & Order'' * ...

in the middle of the thoracic region are heart-shaped and as broad in the anteroposterior as in the transverse direction. At the ends of the thoracic region they resemble respectively those of the cervical and lumbar vertebrae. They are slightly thicker behind than in front, flat above and below, convex from side to side in front, deeply concave behind, and slightly constricted laterally and in front. They present, on either side, two costal demi-facets, one above, near the root of the pedicle, the other below, in front of the inferior vertebral notch; these are covered with cartilage in the fresh state, and, when the vertebrae are articulated with one another, form, with the intervening intervertebral fibrocartilages, oval surfaces for the reception of the heads of the ribs. Thoracic vertebrae

The pedicles are directed backward and slightly upward, and the inferior vertebral notches are of large size, and deeper than in any other region of the vertebral column. The laminae are broad, thick, and imbricated – that is to say, they overlap those of subjacent vertebrae like tiles on a roof and connect with the pedicles to surround and protect the spinal cord. The

intervertebral foramen The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF) is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina. The foramina, or openi ...

is small, and circular, with two at each intervertebral level, one for the right and one for the left exiting nerve roots. The

vertebral foramen In a typical vertebra, the vertebral foramen is the foramen (opening) formed by the anterior segment (the body), and the posterior part, the vertebral arch. The vertebral foramen begins at cervical vertebra #1 (C1 or atlas) and continues inferio ...

is the large opening posterior to the vertebral body also known as the ''spinal canal''. It contains and protects the spinal cord at the thoracic level. The

spinous process 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 ...

is long, triangular on coronal section, directed obliquely downward, arising from the lamina and ending in a tuberculated extremity. These processes overlap from the fifth to the eighth, but are less oblique in direction above and below. The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminae; their articular facets are practically flat, and are directed backward and a little lateralward and upward. The

inferior articular processes The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = " process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent verteb ...

are fused to a considerable extent with the laminae, and project but slightly beyond their lower borders; their facets are directed forward and a little medialward and downward. The transverse processes arise from the arch behind the superior articular processes and pedicles; they are thick, strong, and of considerable length, directed obliquely backward and lateralward, and each ends in a clubbed extremity, on the front of which is a small, concave surface, for articulation with the tubercle of a rib.

Individual thoracic vertebrae

First thoracic vertebra (T1)

The first thoracic vertebra has, on either side of the body, an entire articular facet for the head of the first rib, and a demi-facet for the upper half of the head of the second rib. The body is like that of a cervical vertebra, being broad, concave, and lipped on either side. The superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal. The transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae. The thoracic spinal nerve 1 (T1) passes out underneath it.

Second thoracic vertebra (T2)

The

thoracic spinal nerve 2 The thoracic spinal nerve 2 (T2) is a spinal nerve of the thoracic segment.

(T2) passes out underneath it. The second thoracic vertebra is larger than the first thoracic vertebra

Third thoracic vertebra (T3)

The

thoracic spinal nerve 3 The thoracic spinal nerve 3 (T3) is a spinal nerve of the thoracic segment.sternal angle. The

thoracic spinal nerve 4 The thoracic spinal nerve 4 (T4) is a spinal nerve of the thoracic segment.

(T4) passes out underneath it. Spine Adult Male Age 57

Fifth thoracic vertebra (T5)

The fifth thoracic vertebra, together with the fourth, is at the same level as the sternal angle. The

human trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from the ...

divides into two main

bronchi A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchus. ...

at the level of the 5th thoracic vertebra, but may also end higher or lower, depending on breathing. The

thoracic spinal nerve 5 The thoracic spinal nerve 5 (T5) is a spinal nerve of the thoracic segment.thoracic spinal nerve 6 The thoracic spinal nerve 6 (T6) is a spinal nerve of the thoracic segment The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the v ...

(T6) passes out underneath it.

Seventh thoracic vertebra (T7)

The

thoracic spinal nerve 7 The thoracic spinal nerve 7 (T7) is a spinal nerve of the thoracic segment The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the ve ...

(T7) passes out underneath it.

Eighth thoracic vertebra (T8)

The eighth thoracic vertebra is, together with the ninth thoracic vertebra, at the same level as the

xiphisternum The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Both ...

. The thoracic spinal nerve 8 (T8) passes out underneath it.

Ninth thoracic vertebra (T9)

The ninth thoracic vertebra may have no demi-facets below. In some subjects however, it has two demi-facets on either side; when this occurs the tenth doesn't have facets but demi-facets at the upper part. The

thoracic spinal nerve 9 The thoracic spinal nerve 9 (T9) is a spinal nerve of the thoracic segment.xiphisternum The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Both ...

(or xiphoid process of the sternum) is at the same level in the

axial plane The transverse plane (also known as the horizontal plane, axial plane and transaxial plane) is an anatomical plane that divides the body into superior and inferior sections. It is perpendicular to the coronal and sagittal planes. List of cli ...

Tenth thoracic vertebra (T10)

The tenth thoracic vertebra has an entire articular facet (not demi-facet) on either side, which is placed partly on the lateral surface of the pedicle. It doesn't have any kind of facet below, because the following ribs only have one facet on their heads. The

thoracic spinal nerve 10 The thoracic spinal nerve 10 (T10) is a spinal nerve of the thoracic segment.

(T10) passes out underneath it.

Eleventh thoracic vertebra (T11)

In the eleventh thoracic vertebra the body approaches in its form and size to that of the lumbar vertebrae. The articular facets for the heads of the ribs are of medium size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the thoracic region. The spinous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, and do not have articular facets. The thoracic spinal nerve 11 (T11) passes out underneath it.

Twelfth thoracic vertebra (T12)

The twelfth thoracic vertebra has the same general characteristics as the eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateralward, like those of the lumbar vertebrae; by the general form of the body, laminae, and spinous process, in which it resembles the lumbar vertebrae; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mammillary and accessory processes of the lumbar vertebrae. Traces of similar elevations are found on the transverse processes of the tenth and eleventh thoracic vertebrae. The

thoracic spinal nerve 12 The thoracic spinal nerve 12 (T12) is a spinal nerve of the thoracic segment The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the ...

(T12) passes out underneath it.

Other animals

In other animals the number of thoracic vertebrae can vary greatly; for example, most

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

s have 13, but

koalas The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the womb ...

have only 11. 12 to 15 is common among

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s, with 18 to 20 in

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inh ...

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species ...

es, and

elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...

s, and extremes in mammals are marked by certain

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

s with 25 and

cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

ns with 9.Hyman (1922), p.124

Additional images

File:Thoracic vertebrae animation.gif, Position of thoracic vertebrae. Animation. File:Thoracic vertebrae animation2.gif, Same as the left, but bones around the thoracic vertebrae are shown as semi-transparent. Human thoracic vertebra.stl, 3D image File:Thoracic vertebrae - close-up - animation3.gif, Animation showing the shape of thoracic vertebrae. File:Thoracic vertebrae lateral7.png, Lateral surface of the thoracic vertebrae. Right half of the thoracic skeleton is not shown. File:Illu vertebral column.svg, Vertebral column. File:Gray_111_-_Vertebral_column-coloured.png, Vertebral column. File:Gray303.png, Vertebral arches of three thoracic vertebrae viewed from the front. File:Gray314.png, Section of the costotransverse joints from the third to the ninth inclusive. File:Gray82.png, A typical thoracic vertebra, viewed from above. File:Vertebra toracica.JPG, A thoracic vertebra, viewed from above. File:Vertebra toracica inf.JPG, A thoracic vertebra, viewed from below.

References

External links

Interactive tool to identify parts
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{{Authority control Bones of the thorax Bones of the vertebral column