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the elements of the axial skeleton forming the spine of vertebrate animals and man.

A vertebra consists of a thickened ventral (in man, anterior) part, the vertebral body, and dorsal arch that fuses with the vertebral body and closes the cerebrospinal canal. In fishes, the lower vertebral arches form transversal processes in the truncal segment; the ribs are attached to these processes. In the caudal segment, the lower arches interlock in the hemal arch with the lower spinal process. The upper arch bears an unpaired upper spinal process. At the arch’s base in terrestrial vertebrates are paired anterior and posterior articular processes and a pair of transversal processes with facets for articulating with the tubercle of a rib. The facet for the head of a rib is usually located between two vertebrae, but it may be entirely displaced to the body of the second vertebra or even fuse with the facet for the tubercle of the rib. A vertebra may also have additional processes.

In fishes, some amphibians, and reptiles, the articular surfaces of the vertebrae may be biconcave, or amphicelous. In most amphibians and reptiles, the vertebral bodies become procelous (concave in front and convex in back) or opisthocelous (convex in front and concave in back) because of the need for mobility. The vertebral bodies are heterocelous, or saddle-shaped, in birds. Mammals have intervertebral cartilaginous disks, and consequently the vertebral bodies are platycelous, or flat in front and concave in back.

The vertebral bodies developed independently in different groups of animals. Their multiple origins may be clearly traced in ontogeny and especially in phylogeny. Up to four pairs of ossifications are formed in fishes: two correspond to the bases of the upper (epicentral) and lower (hypocentral) arches and two are pairs of intercalary (pleurocentral) elements. In most fishes the epicenters and hypocenters fused into a ring and the pleuro-centers were reduced. In crossopterygian fishes and many extinct amphibians, for example, the Stegocephalia, the hypocenters formed a crescent-shaped ventral element, paired in crossoptery-gians, with the pleurocenters remaining small and paired. The hypocenters are reduced in most reptiles as in all amniotes. The heads of the ribs, which originally articulated with the hypocenters, occupied a position between the vertebrae after the hypo-centers were lost. The hemal arches and the small lower spinal process fuse with the hypocenters in the caudal region.


References in periodicals archive ?
Over 70 tail vertebrae of both young and adult reptiles, as well as partial tail skeletal remains, were examined by the researchers.
Our work initially revealed the variation character of thoracolumbar vertebrae number, the association of thoracolumbar vertebrae number with carcass trait, and the correlation of VRTN genotype on thoracolumbar vertebrae number.
Moreover, with this surgery, there is no question of bone grafting or damage to natural vertebrae, no need for the post-op long-term cervical collar and a reduced risk of adjacent segment disease.
We did not evaluate the coccygeal vertebrae, because there is known to be abnormal vertebrae in the bulldog tail which are linked to the occurrence of abnormalities in the rest of spinal segments.
The diseased vertebrae and puncture point were determined under the guidance of DSA.
Imai [20] designed Finite Element (FE) models of the trabecular bone of the vertebrae, using 1 mm, 2 mm and 3 mm sized linear tetrahedron elements.
It is known that the body shapes of the cervical vertebrae change with growth.
To address these issues, a new method of age determination using vertebrae has been developed for S.
When the embryo begins to form the upper levels, the genes encoding the formation of cervical vertebrae come off the spool and become activated.
The C2 vertebrae or 'atlas' which carries the skull rotates around the axis when a person turns their head to one side.
Indian doctors fixed his shattered vertebrae in a rare surgery.
For example, if the MRI confirms a bulge or protrusion of the disc along the vertebrae, a 10- or 20-session programme is chalked out to administer physical therapy and manipulate the vertebrae into the right position.