Morphology and distribution of the motor neurons of the accessory nerve (nXI) in the Japanese toad: a cobaltic lysine study.

Motoneurons supplying the accessory nerve (nXI) of the Japanese toad were retrogradely labelled by applying the cobaltic lysine to the cut end of the nerve. They had morphological characteristics and a distribution pattern similar to those of the rostral spinal motoneurons rather than the branchial motoneurons. We propose that the anuran nXI is equivalent to the so-called spinal portion of the nXI of other vertebrates, and both should be regarded as part of the rostral spinal nerves rather than the nerve accessory to the vagus nerve.