Source : Webster's Revised Unabridged Dictionary (1913)

Psalterium \Psal*te"ri*um\, n.; pl. {Psalteria}. [L., a
   psaltery.] (Anat.)
   (a) The third stomach of ruminants. See {Manyplies}.
   (b) The lyra of the brain.

Source : WordNet®

psalterium
     n : the third compartment of the stomach of a ruminant [syn: {omasum},
          {third stomach}]
     [also: {psalteria} (pl)]