Fig. 4. Detailed structure of the psc neurone in untreated and ablated specimens. (A) Five examples of the psc neurone in untreated specimens showing the consistent structure of the central projections. (B) Five examples of the psc neurone following unilateral ablation of the dorsal and lateral groups of neurones. These examples show axon splitting at the entry points as well as duplication of key structures. (C) Five examples of the psc neurone following unilateral ablation of only the dorsal groups of neurones. These examples do not show axon splitting at the entry point but all show defects associated with crossing the midline (*). (D) Five examples of the psc neurone following unilateral ablation of only the lateral groups of neurones. These examples show defects with the formation of the posterior projection. Refer to text for detailed descriptions. Lowercase lettering refers to the identity of the different sub-branches in the psc neurone.