(3) Opisthocoelous, or concave behind, only occasionally found in the thoracic region, e.g.
Opisthocoelous) in the neck and anterior part of the back, where there must have been much freedom of motion.
The bodies of the cervical vertebrae are elongated, strongly keeled, and markedly opisthocoelous, or concave behind and convex in front.
In the trunk vertebrae the opisthocoelous character of the centrum graduall y diminishes.
F, P, This is particularly evident in the case of the Stegocephalians; and recent batrachians, tailed and tailless, show the mode of articulation of the vertebrae,whether amphicoelous, opisthocoelous or procoelous, to be of but secondary systematic importance in dealing with these lowly vertebrates.
Either to the vertebra anterior (procoelous type) or posterior (opisthocoelous type) to it, if not remaining as an independent, intervertebral, ossified sphere, as we sometimes find in specimens of Pelobatidae.
In such cases the distinction between amphicoelous and opisthocoelous vertebrae rests merely on a question of ossi A S FIG.
Amphicoelous (bi-concave) vertebrae are found in the Apoda and in some of the Caudata; opisthocoelous (convexo-concave) vertebrae in the higher Caudata and in the lower Ecaudata; whilst the great majority of the Ecaudata have procoelous (concavo-convex) vertebrae.