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early 17 SNb, focal plane 3 |
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In this focal plane we now see the 13/30 synapse. We are below (external to) muscles 6 and 7, and we can now see the oblique muscles 30, 14, and 28. The ISN and SNa can be see, still out of focus, underneath the SNb (arrows). The ISN normally lies underneath or just posterior to the SNb. While the morphology of the SNb is highly stereotyped, its position relative to the ISN tract is not (see early 17 brightfield for examples). In some segments it is right on top of the ISN, and in others somewhat posterior to it. It is almost never anterior to the ISN, however. The SNa is usually underneath the SNb or just posterior to it. The apparent gap in the pathway (left of SNd in the right-hand segment) is not a gap due to dissection damage, but a section of the pathway that leaves this focal plane. |
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