A flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc. The notochord is found ventral to the neural tube.
Comment:
The notochord appears early in embryogeny and plays an important role in promoting or organizing the embryonic development of nearby structures. In most adult chordates the notochord disappears or becomes highly modified. In some non-vertebrate chordates and fishes the notochord persists as a laterally flexible but incompressible skeletal rod that prevents telescopic collapse of the body during swimming[TOLWEB]; [development-note] "In between vertebra the notochord becomes the nucleus pulposus, under it degenerates, and at anterior end in some species its tissue merges with some of the cranial bones.. Some organisms retain a post-embryonic notochord."; [homology-note] "(...) at some stage of its development, every chordate exhibits five uniquely derived characters or synapomorphies of the group: (...) (3) a stiff, longitudinal rod of turgid cells along the dorsal part of the body that is called a notochord (...).[well established][VHOG]" xsd:string {date_retrieved="2012-09-17", external_class="VHOG:0000199", ontology="VHOG", source="ISBN:978-0030223693 Liem KF, Bemis WE, Walker WF, Grande L, Functional Anatomy of the Vertebrates: An Evolutionary Perspective (2001) p.28", source="http://bgee.unil.ch/"}