Vertebra (ver'te-brah)

One of the o eous segments of which the skeleton proper is made up. It consists typically of a number of o eous pieces definitely arranged so as to form two rings, a dorsal and a ventral, meeting in a common center (the centrum), which inclose respectively the central nervous system and the circulatory organs and viscera, and are known as the neural and hemal arches. cephalic vertebrae. The bones of the skull considered as vertebral in type. cervical vertebrae. The anterior or superior seven of the vertebrae, the two nearest the skull being termed the atlas and axis. They have the transverse proce es perforated for the vertebral artery, the spinous proce short and bifid and the lumen of the neural arch somewhat triangular and larger than in the dorsal or lumbar vertebrae, coccygeal vertebrae. The vertebrae of the coccygeal region. They are rudimentary, commonly four in number, sometimes five, seldom three, cranial vertebrae. Vertebrae whose component parts consist of cranial bones and the o eous and cartilaginous appendages of the skull. The theory of their existence was advanced by Goethe and Oken and elaborated by Cuvier and Sir Richard Owen. Their homology with true vertebrae is no longer accepted on embryological evi- 872 dence, dorsal vertebrae. See thoracic vertebrae. lumbar vertebrae. The five vertebrae which lie above or anterior to the sacrum. They lack costal articular surfaces, and the transverse diameter of their bodies is greater than the anteroposterior, sacral vertebrae. The segments, five in number, which in adult life fuse to form the sacrum, thoracic vertebrae. The vertebrae, twelve in number, with which the ribs articulate. They are especially characterized by articular surfaces for the ribs, downward sloping spinous proce es, and a small circular lumen of the neural arch. [Lat., vertebra, joint, from vertere, to turn.]