The Chordata is the animal phylum with which everyone is most intimately familiar, since it includes humans and other vertebrates. However, not all chordates are vertebrates. All chordates have the following features: pharyngeal slits, dorsal nerve cord, notochord, and post-anal tail. Pharyngeal slits are a series of openings that connect the inside of the throat to the outside of the "neck". These are often, but not always, used as gills. Dorsal nerve cord is a bundle of nerve fibers which runs down the "back". It connects the brain with the lateral muscles and other organs. A notochord is a cartilaginous rod running underneath, and supporting, the nerve cord. A post-anal tail is an extension of the body past the anal opening.