Notochord
All chordates possess a notochord, or a type of flexible support rod, at some point in their development. In this dissected lungfish, which is a member of the chordates, tissues have been dissected away to display the notochord.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"Lungs of Protopterus dolloi."
http://en.wikipedia.org/wiki/File:Lungs_of_Protopterus_dolloi.JPG
Wikipedia
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