The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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The notochord is a cylindrical column of cells that appears early in embryonic development. The notochord forms on the dorsal side of the embryo and establishes a bilateral longitudinal axis of development before the formation of the neural tube and spinal vertebrae. The formation of the notochord is a common and uniting factor of all chordate animals. In humans, cells forming the notochord later become part of the vertebrae, nasopharynx, and skull.
In the early developmental stages of all vertebrates, a notochord forms within the embryonic disk. The notochord lies between the ectoderm and endoderm. The rod of cells forms between the primitive knot and the prechordal plate of cells.
As mesoderm forms, aggregations (clumps or blocks) of cells, derived from mesoderm, form somites along the sides of the notochord. Depending on their level these mesodermal somites ultimately develop into vertebra, ribs, muscles, and dermal structures.
Formation of the notochord is critical to the proper formation and organization of the neural plate, neural folds, and subsequent development of the brain and other neural structures. One of the classic experiments in developmental biology, the organizer experiment, showed that in amphibian embryos, cells taken from the notochordal region of one embryo could induce neural structure formation when grafted on to a second embryo.