The neural arches, in this caudal region, are borne only on alternate centra. Other fishes display the Diplospondylous condition, but duplicate the neural arches only, still others duplicate both arches and centra. Amphibia Note four vertebral regions, cervical, trunk, sacral and caudal. Note particularly that both cervical and sacral regions each consist of only one vertebra. Compare ribs in Frog and Necturus.
Reptiles Note five vertebral regions, cervical, thoracic, lumbar, sacral and caudal.
Compare the vertebral columns of Alligator, Snake and Turtle. Moveable, double-headed, ribs are borne on the thoracic vertebrae. Ribs, if present on the lumbar vertebrae are fused. Snakes may have as many as 500 vertebrae. Both thoracic and lumbar regions bear ribs.