The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates.
From the en.wikipedia.org
In living amphibians, there is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods.
From the en.wikipedia.org
The heaviest and longest of them all may have been Amphicoelias fragillimus, known only from a now lost partial vertebral neural arch described in 1878.