Basic structure of a thoracic vertebra
Like most bones of the vertebral column, each thoracic vertebra has a standard set of anatomical structures. The main elements include:
- Vertebral body (corpus vertebrae). Moving from the upper thoracic vertebrae to the lower ones, the body gradually increases in size. The lower thoracic vertebrae (T₁₀–T₁₂) closely approach lumbar vertebrae in their shape and massiveness. On the intervertebral surface of the body (facies intervertebralis), there is the anular epiphysis (epiphysis anularis).
- Vertebral arch (arcus vertebrae). Consists of the pedicle of the vertebral arch (pediculus arcus vertebralis) and the lamina of the vertebral arch (lamina arcus vertebrae).
- Vertebral foramen (foramen vertebrale). In the thoracic region, it gradually decreases in size from top to bottom and usually has a rounded-triangular shape.
- Processes. Several processes extend from the arch: one spinous (processus spinosus), two transverse (processus transversus), and four articular — superior and inferior (processus articularis superior and inferior).
- Notches. At the junction of the body and the arch are the superior and inferior vertebral notches (incisura vertebralis superior and inferior). When two adjacent vertebrae articulate, these notches form the intervertebral foramen (foramen intervertebrale).
Costal facets: the main feature of the region
It is the thoracic region that provides a movable connection with the rib cage. For this purpose, specific articular surfaces are provided on the bones — costal facets.
There are several variants of such facets depending on how the rib attaches to the spine:
- Complete costal facet on the body (fovea costalis). This is the mark of direct contact between the head of the rib and the body of a specific vertebra.
- Costal demifacets on the body (fovea costalis superior and inferior). They are formed when the head of a single rib articulates not with one, but with the bodies of two adjacent vertebrae at once. In this case, an inferior demifacet is formed on the upper vertebra, and a superior demifacet on the lower one.
- Costal facet of the transverse process (fovea costalis processus transversi). Designed for articulation with the tubercle of the rib. It is present on the transverse processes from the first to the tenth thoracic vertebra (T₁–T₁₀). The eleventh and twelfth vertebrae (T₁₁–T₁₂) lack this facet, as the last two ribs have no tubercles.
Classification: how to distinguish thoracic vertebrae
By the location and number of costal facets on the body, one can precisely determine which vertebra is before us. This is a key skill for understanding the osteology of the thoracic region.
- First thoracic vertebra (T₁). Has one complete facet on the upper part of its body (for the head of rib I) and one inferior demifacet (for the upper half of the head of rib II).
- From the second to the ninth (T₂–T₉). These are typical representatives of the region. Their bodies bear two demifacets: superior and inferior (for articulation with the heads of ribs II–X, respectively).
- Tenth vertebra (T₁₀). Its body has only a superior demifacet intended for rib X. The articular facet on the transverse process (fovea costalis proc. transversi) is still present.
- Eleventh and twelfth (T₁₁–T₁₂). The bodies of these vertebrae feature complete costal facets (for the XI and XII ribs). At the same time, their transverse processes lack facets entirely.
Spatial orientation of the vertebra
To properly hold the bone in your hands and determine its position in the human body, follow a simple algorithm:
- Point the spinous process backward. In thoracic vertebrae, it is long, pointed, and directed obliquely downwards (this is especially pronounced in the midthoracic region).
- Determine top and bottom by the articular surfaces of the processes (processus articulares). In the thoracic region, they are oriented almost in the frontal plane: the superior articular surfaces face backward, and the inferior ones look forward, toward the vertebral body.
- Examine the nature of the costal facets (complete or demifacets, presence of a facet on the transverse process) to establish the exact number of the vertebra.
To remember the facets on the vertebral bodies: T1 — "one and a half" (one complete and a lower half); T2–T9 — "two halves"; T10 — "one upper half"; T11–T12 — "one complete each".
Class and exam questions
Why do the XI and XII thoracic vertebrae lack facets on their transverse processes?
The articular facet on the transverse process is required for articulation with the rib tubercle. The XI and XII ribs lack tubercles, and therefore the corresponding facets on the transverse processes of the T₁₁ and T₁₂ vertebrae are also absent.
How are the articular surfaces oriented in thoracic vertebrae?
They are oriented almost in the frontal plane. The superior articular surfaces face backward, and the inferior ones face forward (toward the vertebral body).
What forms the intervertebral foramen?
The intervertebral foramen (foramen intervertebrale) is formed by the junction of the superior vertebral notch of the lower vertebra and the inferior vertebral notch of the upper one.
What else to study on this topic
- Structure of the vertebral arch: pedicles and laminae
- Formation of intervertebral foramina
- Features of cervical and lumbar vertebrae
- Anatomy of the ribs (head, neck, tubercle)
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