Thoracic vertebrae

Thoracic vertebrae
Position of the thoracic vertebrae (shown in red). In human, thoracic vertebrae consists of 12 bones. From top to down, T1, T2, …, T12.
A typical thoracic vertebra, seen from lateral side.
Details
Identifiers
Latin	vertebrae thoracicae
MeSH	D013904
TA98	A02.2.03.001
TA2	1058, 1059
FMA	9139
Anatomical terms of bone

In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae.^[1] In humans, there are twelve thoracic vertebrae 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 a lot larger than the upper. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the transverse processes 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 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 vertebra

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 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 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 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 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

The first and ninth through twelfth thoracic vertebra have some peculiarities

Fourth thoracic vertebra (T4)

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

The thoracic spinal nerve 4 (T4) passes out underneath it.

A thoracic spine X-ray of a 57-year-old male.

Surface orientation of T3 and T7, at middle of spine of scapula and at inferior angle of the scapula, respectively.

Other animals

In other animals the number of thoracic vertebrae can vary greatly;^[2] for example, most marsupials have 13, but koalas have only 11.^[3] 12 to 15 is common among mammals, with 18 to 20 in horses, tapirs, rhinoceroses, and elephants, and extremes in mammals are marked by certain sloths with 25 and cetaceans with 9.^[4]

Additional images

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  Position of   thoracic vertebrae. Animation.
• 
  Same as the left, but bones around the thoracic vertebrae are shown as semi-transparent.
• 
  3D image
• 
  Animation showing the shape of    thoracic vertebrae.
• 
  Lateral surface of the    thoracic vertebrae. Right half of the thoracic skeleton is not shown.
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  Vertebral column.
• 
  Vertebral column.
• 
  Vertebral arches of three thoracic vertebrae viewed from the front.
• 
  Section of the costotransverse joints from the third to the ninth inclusive.
• 
  A typical thoracic vertebra, viewed from above.
• 
  A thoracic vertebra, viewed from above.
• 
  A thoracic vertebra, viewed from below.

See also

• Costovertebral articulations
• Vertebral column
• Cervical vertebrae
• Lumbar vertebrae

References

This article incorporates text in the public domain from page 102 of the 20th edition of Gray's Anatomy (1918)

External links

Wikimedia Commons has media related to Thoracic vertebrae.

• Interactive tool to identify parts
• thoraxbones at The Anatomy Lesson by Wesley Norman (Georgetown University)
• Photos at University of Utah
• SpineUniverse anatomical diagram