In the existing Proteidea, and in the
Gymnophiona, the
vertebral centra are amphicoelous. In the
Salamandridea they are opisthocoelous. In
Pipa and
Bombinator they are
also opisthocoelous, but in other Batrachia they are, for the
most part, procoelous, but vary in different regions, some
being biconvex and some biconcave.
The first vertebra, or atlas, presents two articular cups to
the condyles of the skull, but there is no specially modified
axis vertebra.
The transverse processes may be simple, but in the Labyrinthodonts,
and in the existing Salamanders, they are divided
into two processes - an upper
tubercular, and a lower
capitular,
process. When the transverse process is thus divided, the
proximal end of the rib is correspondingly split into a capitular
and a tubercular process.