The nematode Caenorhabditis elegans possesses a simple embryonic nervous system comprising 222 neurons, a number small enough that the growth of each cell could be followed to provide a systems-level view of development. However, studies of single cell development have largely been conducted in fixed or pre-twitching live embryos, because of technical difficulties associated with embryo movement in late embryogenesis. We present open source untwisting and annotation software which allows the investigation of neurodevelopmental events in post-twitching embryos, and apply them to track the 3D positions of seam cells, neurons, and neurites in multiple elongating embryos. The detailed positional information we obtained enabled us to develop a composite model showing movement of these cells and neurites in an "average" worm embryo. The untwisting and cell tracking capability we demonstrate provides a foundation on which to catalog C. elegans neurodevelopment, allowing interrogation of developmental events in previously inaccessible periods of embryogenesis.