The Collaborative International Dictionary of English v.0.48:

Rhinencephalon \Rhi`nen*ceph"a*lon\
   (r[imac]`n[e^]n*s[e^]f"[.a]*l[o^]n), n.; pl. Rhinencephala
   (r[imac]`n[e^]n*s[e^]f"[.a]*l[.a]). [NL., fr. Gr. "ri`s,
   "rino`s, the nose + 'egke`falos the brain.] (Anat.)
   The division of the brain in front of the prosencephalon,
   consisting of the two olfactory lobes from which the
   olfactory nerves arise.
   [1913 Webster]

   Note: The term is sometimes used for one of the olfactory
         lobes, the plural being used for the two taken
         together.
         [1913 Webster]