Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
"The first thoracic vertebra is a transitional vertebra. The body in its general conformation approaches very closely the seventh cervical, in that the greatest diameter is transverse, and its upper surface is concave from side to side. On each side is an entire pit, close to the upper border, for the head of the first rib, and a very small pit (inferior costal pit) below for the head of the second rib. The spinous process is thick, strong, almost horizontal and usually more prominent than that of the seventh cervical, an important point to remember when counting the spines on the living subject."
"The ninth has superior costal pits, and usually no inferior; when the inferior pits are present, this vertebra is not exceptional."
"The tenth usually has an entire costal pit at its upper margin, on each side, but occasionally only a superior costal pit. It has no lower pits and the pits on the transverse processes are usually small."
"The eleventh has a large body resembling that of a lumbar vertebra. The pits are on the pedicles and they are complete and of large size. The transverse processes are short, show evidence of subdivision into three parts, and have no pits for the tubercles of the eleventh pair of ribs."
"In many mammals, the spines of the anterior verebrae are directed backward, and those of the posterior directed forward, whilst in the center of the column there is usually one spine vertical. The latter is called the anticlinal vertebra, and indicates the point at which the thoracic begin to assume the characters of lumbar vertebrae. In man the eleventh thoracic is the anticlinal vertebra."
"The twelfth resembles in general characters the eleventh, but may be distinguished from it by the articular surfaces on the inferior articular processes being convex and turned laterally as in the lumbar vertebrae. The transverse process is rudimentary and tripartite, presenting for examination three tubercles, superior, inferior, and lateral, which corresponds respectively to the mammillary, accessory, and transvere processes of a lumbar vertebra. There is one complete pit on the root (pedicle) for the head of the twelfth rib."
"The twelfth thoracic, in the absence of the twelfth pair of ribs, commonly conforms to the type of a lumbar vertebra. A peculiarity, more frequent in the thoracic and lumbar than in the cervical and sacral regions of the column, is the existence of a half-vertebra. Such specimens have a wedge-shaped half-centrum, to which are attached a lamina, a transverse, superior, and inferior articular, and half a spinous process. As a rule, a half-vertebra is ankylosed to the vertebrae above and below."
Redrawn from Terry, R.J. in Jackson, C.M., Ed. Morris' Human Anatomy, 9th Ed. P. Blakiston's Son & Co., Philadelphia, 1933.
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