Notochord

The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoblast and defining the primitive axis of the embryo. In lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it is replaced by the vertebral column.

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Its appearance synchronizes with that of the neural tube. On the ventral aspect of the neural groove an axial thickening of the endoderm takes place; this thickening assumes the appearance of a furrow (the chordal furrow) the margins of which come into contact, and so convert it into a solid rod of cells (the notochord) which is then separated from the endoderm.

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In higher vertebrates, it extends throughout the entire length of the future vertebral column, and reaches as far as the anterior end of the mid-brain, where it ends in a hook-like extremity in the region of the future dorsum sell? of the sphenoid bone. It lies at first between the neural tube and the endoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medial-ward and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull and vertebral column, and the membranes of the brain and medulla spinalis are developed.

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Embryo: : For musical bands with the name "Embryo" see Embryo (band)...

Cell: A cell is a single unit or compartment, enclosed by a border or wall. A cell is usually part of a larger structure. More specific meanings depend on the context in which the work is used....

Vertebral column: The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen....