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Definition of Rhachis


  1. The spine.
  2. The continued stem or midrib of a pinnately compound leaf, as in a rose leaf or a fern.
  3. The principal axis in a raceme, spike, panicle, or corymb.
  4. The shaft of a feather. The rhachis of the after-shaft, or plumule, is called the hyporhachis.
  5. The central cord in the stem of a crinoid.
  6. The median part of the radula of a mollusk.
  7. A central cord of the ovary of nematodes.