In developing marsupials, the path taken through
the optic chiasm by ipsilaterally projecting retinal ganglion
cells is complicated. Just prior to entry into the chiasm,
ganglion cells destined for the ipsilateral optic tract
separate from the remainder of axons by turning abruptly
downwards to take a position in the ventral part of the
optic nerve. In this report, it is shown that a discrete
population of about 10–15 large glial cells transiently
form a linear array across the prechiasmatic part of the
optic nerve, precisely at this axon turning point. The
distinct morphology of these cells and their novel location
may reflect a specialized role in axon guidance.