Morphology of the caudal spinal cord in Rana (ranidae) and Xenopus (pipidae) tadpoles

Kiisa Nishikawa, Richard Wassersug

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Using a variety of neuroanatomical and histological techniques, we compare the spinal cord and peripheral nerve distribution in the tails of larvae from Xenopus laevis and three species of Rana. The relatively large, postsacral spinal, cord of Xenopus contains abundant motoneurons and their axons. Spinal nerves exit from the spinal cord in a regular array, one nerve per myotome, from the cervical region to near the end of the tail. Somata of motoneurons innervating caudal myotomes are found along the entire length of the tail. In contrast, the caudal cord of Rana is reduced to a filum terminate consisting of little more than an ependymal tube; spinal nerves to all caudal myotomes leave the cord in the sacral region and reach their motor targets via a cauda equina and caudal plexus. Motoneuron cell bodies innervating caudal myotomes are found only in the sacral region. The Rana larval pattern is similar to that of adult frogs and mammals, whereas the Xenopus larval pattern is more like that of salamanders and reptiles. These gross neuroanatomical differences are not due to differences in the size or developmental stage of the tadpoles, but instead are associated with differences in the swimming behavior of the larvae. The presence of motoneurons in the caudal spinal cord of Xenopus may provide local intermyotomal control within the tail; the elongated topography of the cord appears to permit finer, rostral‐to‐caudal regulation of neuromuscular activity. The Rana spinal cord, on the other hand‐with motoneurons clustered anteriorly‐may produce concurrent firing of adjacent ipsilateral myotomes, but at the expense of fine intermyotomal regulation. The fact that nerves in the tail of Xenopus enter and exit from the spinal cord locally, as opposed to far anteriorly as in Rana, means that for tadpoles of the same size, reflex arc lengths are many times shorter in Xenopus.

Original languageEnglish (US)
Pages (from-to)193-202
Number of pages10
JournalJournal of Comparative Neurology
Issue number2
StatePublished - Mar 8 1988


  • amphibians
  • locomotion
  • motoneurons
  • myotomes
  • tail

ASJC Scopus subject areas

  • General Neuroscience


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