NeuroFIG 5: Composition and placement of dorsal cord (DC) and ventral nerve cord (VNC).

Composition and placement of dorsal cord (DC) and ventral nerve cord (VNC). Top illustration indicates the approximate section levels for the TEMs that are shown.
A–D. Sections through the VNC. In all panels, arrows indicate AVM process running at the extreme ventral region of the VNC. E. Section through the DC. All are transverse sections, and the nerve bundles and cell bodies in all sections are indicated by dotted red lines. Bars, 1 μm.
A. Immediately posterior to the nerve ring, at the anterior ventral ganglion, all the processes coalesce into a thick, single bundle. Anterior to this region, processes enter the ring from either the right or the left side. Cephalic sheath cells wrap around the cord on the ventral and lateral sides. (Asterisks) Excretory gland processes that terminate in the ventral regions of the NR. (Image source: [MRC] N2U[VC]-208-20a.)
B. Posterior to the ventral ganglion, the excretory pore splits the VNC into two bundles of approximately equal thickness. (Image source: [MRC] N2U[VC]-222-17a.)
C. Posterior to the pore, the nerve fibers gradually cross (decussate) from the left side to the right of the ventral hypodermal ridge (Hyp). Arrowheads indicate two such neurites in the process of crossing over the midline. (Image source: [MRC] N2U[VC]-228-12a.)
D. Slightly more posteriorly, the VNC is composed of a thin left bundle and a thick right one separated by the ventral hypodermal ridge. Cell bodies of RVG neurons are located dorsal to the right bundle. (hmc) Head mesodermal cell; (Ps) pseudocoleomic cavity. (Image source: [MRC] N2U[VC]-241-7a.)
E. The DC is positioned on the left side of the dorsal hypodermal ridge. Commissures that reach the dorsal side from the right must cross the midline over the hypodermal ridge to reach the DC. (Amsh) Amphid sheath; (Hyp) hypodermal ridge. (Image source: [MRC] N2U[DC]-213-18a.)

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