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n. pl. sple·ni·i (-nē-ī′)
Either of two muscles of the back of the neck, extending from the upper vertebrae to the base of the skull, that rotate and extend the head and neck.
[New Latin splēnius, from Latin splēnium, patch, plaster (from its shape), from Greek splēnion, from splēn, spleen.]
sple′ni·al (-nē-əl) adj.