| Thoracic vertebrae | |
|---|---|
 Position of the thoracic vertebrae (T1–T12) | |
 Animation of T2 | |
| Details | |
| Identifiers | |
| Latin | vertebrae thoracicae |
| MeSH | D013904 |
| TA98 | A02.2.03.001 |
| TA2 | 1059 |
| FMA | 9139 |
| Anatomical terms of bone | |
Invertebrates,thoracic vertebrae compose the middle segment of thevertebral column, between thecervical vertebrae and thelumbar vertebrae.[1] In humans, there are twelve thoracicvertebrae of intermediate size between the cervical and lumbar vertebrae; they increase in size going towards the lumbar vertebrae.[citation needed] They are distinguished by the presence offacets on the sides of the bodies forarticulation with theheads of the ribs, as well as facets on thetransverse processes of all, except the eleventh and twelfth, for articulation with thetubercles 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.
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.
Thevertebral 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.
Thepedicles 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.
Thelaminae 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.
Theintervertebral foramen is small, and circular, with two at each intervertebral level, one for the right and one for the left exiting nerve roots.
Thevertebral foramen is the large opening posterior to the vertebral body also known as thespinal canal. It contains and protects the spinal cord at the thoracic level.
Thespinous 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.
Thesuperior 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.
Theinferior articular processes are fused to a considerable extent with the laminae, and project slightly beyond their lower borders; their facets are directed proximally, medially, and inferiorly to the lamina.
Thetransverse 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.
The first thoracic vertebra has, on either side of thebody, 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.
Thesuperior articular surfaces are directed upward and backward; thespinous process is thick, long, and almost horizontal.
Thetransverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae.
Thethoracic spinal nerve 1 (T1) passes inferior to it.
Thethoracic spinal nerve 2 (T2) passes inferior to it.The second thoracic vertebra is larger than the first thoracic vertebra
Thethoracic spinal nerve 3 (T3) passes inferior to it.
The fourth thoracic vertebra, together with the fifth, is at the same level as thesternal angle.
Thethoracic spinal nerve 4 (T4) passes inferior it.
The fifth thoracic vertebra, together with the fourth, is at the same level as thesternal angle. Thehuman trachea divides into two mainbronchi at the level of the 5th thoracic vertebra, but may also end higher or lower, depending on breathing.
Thethoracic spinal nerve 5 (T5) passes inferior to it.
Thethoracic spinal nerve 6 (T6) passes inferior to it.
Thethoracic spinal nerve 7 (T7) passes inferior to it.
The eighth thoracic vertebra is, together with the ninth thoracic vertebra, at the same level as thexiphisternum.
Thethoracic spinal nerve 8 (T8) passes inferior to it.
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.
Thethoracic spinal nerve 9 (T9) passes inferior to it.
Thexiphisternum (or xiphoid process of the sternum) is at the same level in theaxial plane.
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.
Thethoracic spinal nerve 10 (T10) passes inferior to it.
In the eleventh thoracic vertebra thebody 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.
Thespinous process is short, and nearly horizontal in direction.
Thetransverse processes are very short, tuberculated at their extremities, and do not have articular facets.
Thethoracic spinal nerve 11 (T11) passes inferior to it.
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.
Thethoracic spinal nerve 12 (T12) passes inferior to it.
In other animals the number of thoracic vertebrae can vary greatly;[2] for example, mostmarsupials have 13, butkoalas have only 11.[3] 12 to 15 is common amongmammals, with 18 to 20 inhorses,tapirs,rhinoceroses, andelephants, and extremes in mammals are marked by certainsloths with 25 andcetaceans with 9.[4]
This article incorporates text in thepublic domain frompage 102 of the 20th edition ofGray's Anatomy(1918)
