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notochord

notochord (nō´təkôrd´), in biology, supporting rod running most of the length of animals of the phylum Chordata and present at varying times in the life cycle. Composed of large cells packed within a firm connective tissue sheath, the notochord lies between the neural tube (spinal cord) and the gut. The division of the phylum Chordata into subphyla is based on the structure of the notochord and the time of life in which it is present: In the subphylum Urochordata (tunicates) the notochord characterizes the larval, swimming, stage of the animals and does not extend into the head; in the subphylum Cephalochordata (lancelets) the notochord extends to the extreme tip of the head in both young and adults; and in the subphylum Vertebrata the notochord becomes surrounded by skeletal vertebrae during embryonic development—in higher vertebrates it is present in the early embryo only and is later completely replaced by the vertebrae.

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notochord

notochord (chorda dorsalis) A some what flexible, rod-like structure, composed of disc-like, turgid cells, which extends virtually the entire length of the body of adult and/or larval members of the phylum Chordata. Lying below the nerve cord, but dorsal to the intestine, the notochord provides a form of flexible support to the body. In vertebrates the notochord is replaced wholly or partly by the vertebral column, but it is retained throughout life in Cephalochordata and Agnatha.

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notochord

notochord (chorda dorsalis) Somewhat flexible, rod-like structure, composed of disc-like, turgid cells, which extends virtually the entire length of the body of adult and/or larval members of the phylum Chordata. Lying below the nerve cord, but dorsal to the intestine, the notochord provides a form of flexible support to the body. In vertebrates the notochord is replaced wholly or partly by the vertebral column, but it is retained throughout life in Cephalochordata and Agnatha.

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notochord

notochord An elastic skeletal rod lying lengthwise beneath the nerve cord and above the alimentary canal in the embryos or adults of all chordate animals (see Chordata). Its function is to strengthen and support the body and act as a protagonist for the muscles. It is found in both adult and larval lancelets but in adult vertebrates it is largely replaced by the vertebral column.

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notochord

notochord In chordates, such as acorn worms, and the early embryonic stages of vertebrates, the flexible, primitive backbone; in mature vertebrates it is replaced by the spine.

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