prothorax

from WordNet (r) 3.0 (2006)

prothorax
    n 1: the anterior part of an insect's thorax; bears the first
         pair of legs

from The Collaborative International Dictionary of English v.0.48

Prothorax \Pro*tho"rax\, n. [Pref. pro- + thorax.] (Zool.)
   The first or anterior segment of the thorax in insects. See
   Illusts. of {Butterfly} and {Coleoptera}.
   [1913 Webster]