Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems: Vertebral column

Thoracic Vertebrae

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The body of the first thoracic vertebra may bear, on one or both sides, two costal pits resembling the usual thoracic type. The articulation of the head of the first rib is completed by a costal pit on the body of the seventh cervical vertebra. In rare cases the first thoracic rib may be rudimentary and similar in appearance to cervical ribs. The body of the second thoracic vertebra usually exhibits an identifying tubercle marking the attachment of a fasciculus of the medial portion of the longus colli muscle (Krmpotic). The twelfth thoracic vertebra, in the absence of the twelfth pair of ribs, commonly conforms to the lumbar type. The transverse process of the tenth may lack a facet for costal articulation. The lumbar form of transverse process may be present in the eleventh thoracic vertebra. In addition, the transition from the thoracic to the lumbar type of articular process may occur in the eleventh thoracic instead of in the twelfth thoracic vertebra. The transverse processes of the tenth through twelfth transverse processes are distinctly variable and may present evidence of subdivision into three parts. The tripartite transverse processes may possess three tubercles: superior, inferior and lateral, that correspond respectively to the mammillary, accessory, and transverse processes of a lumbar vertebra. There are no transverse costal pits on the transverse processes of the eleventh and twelfth vertebrae. The articular processes may be of the lumbar type on one side and thoracic on the other side, resulting in an asymmetry in the articulation.

Occasionally, a half-vertebra is found in the thoracic and lumbar regions and very rarely in cervical and sacral vertebrae. Such specimens have a wedge-shaped half-body, a half arch with a transverse process, superior and inferior articular processes, and half a spinous process. The half-vertebra is, as a rule, ankylosed to adjacent vertebrae.

The Variable Thoracic Vertebrae

Peculiar Thoracic Vertebrae

Congenital Absence of Dorsal Arches of the Fourth to Seventh Thoracic Vertebrae

A Divided Thoracic Vertebra (after Turner)

Scoliosis

References

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