380 MAMMALIA. 



the most specialized rodents and are most universal in the 

 existing fauna. As in the higher Ungulata, the jugal bone of 

 the zygomatic arch in the skull is supported by the maxilla. 

 Otherwise the cranial characters are much like those of the 

 Sciuromorpha. Typical skulls are known from the Upper 

 Eocene of Europe (Cricetodon) and from the Lower Miocene 

 (White River Formation) of North America (Eumys}. Various 

 remains from superficial deposits also indicate that several of 

 the existing genera and species had a much wider range in 

 Europe during the Pleistocene period than at the present day. 

 Of the Muridae, the lemmings (Myodes lemmus and Cuniculus 

 torquatus), for example, wandered into the British area. A 

 comparatively large animal (skull 0'07 m. in length), generally 

 supposed to have been a dormouse, also lived in Malta (Leithia 

 melitensis). 



ORDER 6. CARNIVORA. 



As already mentioned (p. 287), it is difficult among the 

 earliest Eocene mammals to distinguish the forerunners of 

 the Ungulata from those of the Unguiculata (or claw-bearing 

 groups). Before the close of the Eocene period, however, not 

 only the former but also the latter had become well diffe- 

 rentiated ; and the Carnivora and Insectivora, at least in 

 Europe, had already diverged into their main lines of develop- 

 ment, which have since become more distinctly separated. 



Sub-Order 1. Creodonta (or Carnivora Primigenia). 



The primitive Carnivora are usually grouped in a sub-order 

 named Creodonta (flesh-teeth), but their characters are 

 almost identical with those of the Condylarthra. The only 

 differences seem to be that (i.) the skull has more nearly the 

 aspect of that of a carnivore, (ii.) the teeth are usually more 

 trenchant, and (iii.) the ungual phalanges are always claw- 

 shaped. The head is large compared with the trunk and 

 limbs ; while the lumbar region of the vertebral column is 

 made rigid by the complication of the zygapophyses. The 

 third trochanter of the femur is comparatively small, and the 



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