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DictionarySeevertebraVertebrae
Vertebrae 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. V. B. SUKHANOV Vertebrae
vertebra (ver'te-bra) plural.vertebrae [L.] Any of the 33 bony segments of the spinal column: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae. In adults, the five sacral vertebrae fuse to form a single bone, the sacrum, and the four rudimentary coccygeal vertebrae fuse to form the coccyx. A typical vertebra consists of a ventral body and a dorsal or neural arch. In the thoracic region, the body bears on each side two costal pits for reception of the head of the rib. The arch that encloses the vertebral foramen is formed of two roots or pedicles and two laminae. The arch bears seven processes: a dorsal spinous process, two lateral transverse processes, and four articular processes (two superior and two inferior). A deep concavity, the inferior vertebral notch, on the inferior border of the arch provides a passageway for a spinal nerve. The successive vertebral foramina form the vertebral, or spinal, canal that encloses the spinal cord. The bodies of successive vertebrae articulate with one another and are separated by intervertebral disks, disks of fibrous cartilage enclosing a central mass, the nucleus pulposus. The inferior articular processes articulate with the superior articular processes of the next succeeding vertebra in the caudal direction. Several ligaments (supraspinous, interspinous, anterior and posterior longitudinal, and the ligamenta flava) hold the vertebrae in position, yet permit a limited degree of movement. Motions of the vertebral column include forward bending (flexion), backward bending (extension), side bending (lateral flexion), and rotation. Lateral flexion and rotation motions are coupled so that whenever the vertebrae bend to the side, they also rotate and vice versa. See: sacrum for illus basilar vertebraThe lowest of the lumbar vertebrae.cervical vertebraOne of the seven vertebrae of the neck.coccygeal vertebraOne of the rudimentary vertebrae of the coccyx.vertebra dentataThe second cervical vertebra.false vertebraFixed vertebra.fixed vertebraThe sacral and coccygeal vertebrae that fuse to form the sacrum and coccyx.lumbar vertebraOne of the five vertebrae between the thoracic vertebrae and the sacrum.vertebra magnaSacrum.odontoid vertebraAxis (2).vertebra prominensThe seventh cervical vertebra.sacral vertebraOne of the five fused vertebrae forming the sacrum. See: sacrum for illussternal vertebraOne of the segments of the sternum.thoracic vertebraOne of the 12 vertebrae that connect the ribs and form part of the posterior wall of the thorax. See: spinal column for illustrue vertebraOne of the vertebrae that remain unfused through life: the cervical, thoracic, and lumbar.VertebraeBones in the cervical, thoracic, and lumbar regions of the body that make up the vertebral column. Vertebrae have a central foramen (hole), and their superposition makes up the vertebral canal that encloses the spinal cord.Mentioned in: Achondroplasia, Cerebrospinal Fluid (CSF) Analysis, Cervical Spondylosis, Coccyx Injuries, Sciatica |