Section Ii.--Myomorpha, or Rat-Like Rodents.

Molar dentition from 3--3/3--3 to 6--6/6--6, the former being the usual number; the tibia and fibula are united for at least a third of their length. The zygomatic arch is slender, and the malar process rarely extends so far forward as in the preceding section, and is generally supported below by a continuation of the maxillary zygomatic process; collar bones are perfect (except in Lophiomyidae); upper lip and muffle as in the last; tail cylindrical, sometimes hairy, but commonly covered with scales arranged in rings. Seven families.