Dorsal nerve cord
The dorsal nerve cord is an anatomical feature found in chordate animals, mainly in the subphylum Vertebrata. It is one of the five embryonic features unique to all chordates, the other four being a notochord, a post-anal tail, an endostyle, and pharyngeal slits. The dorsal nerve cord is located dorsal to the notochord and thus also to the gut tube (hence the name). It is formed from clustered neuronal differentiation at the axial region of the ectoderm, known as the neural plate. During embryonic development, the neural plate first invaginates longitudinally to form the neural groove, and the edges of the groove fuse over to form a hollow neural tube. This is an important feature as it distinguishes chordates from other invertebrate phyla such as annelids and arthropods, who have solid nerve cords that are located ventral to the gut tube that are often separated into a series of ladder-like segmental ganglia. The process by which neural tube is performed from the ectoderm is called neurulation. The evolutionary explanation to this adaptation from a solid cord to a hollow tube is unknown. In vertebrates, the dorsal nerve cord (and the subsequent neural tube) gives rise to the brain (via vesicular