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