start stage end stage RoP motor neuron A primary motoneuron that is part of the spinal cord. The axon of the CaP motoneuron on emerging from the ventral root. At the horizontal septum, however, the RoP axon turns laterally to extend within the horizontal septum to the lateral surface of the muscle. 2009-06-18T04:05:40Z TAO:0005180 rostral primary motoneuron ZFA:0005180 zebrafish_anatomy This term is a leaf node in the zebrafish AO and is not in the CL. Ceri primary motor neuron segmentation:14-19 somites adult