The Collaborative International Dictionary of English v.0.48:

Lytta \Lyt"ta\ (l[i^]t"t[.a]), n.; pl. Lytt[ae] (-t[=e]). [L.,
   a worm said to grow under the tongue of dogs, and to cause
   canine madness, fr. Gr. ly`tta, ly`ssa, lit., madness.]
   (Anat.)
   A fibrous and muscular band lying within the longitudinal
   axis of the tongue in many mammals, as the dog.
   [1913 Webster]