442 THE ANATOMY OF VEETEBRATED ANIMALS. 



bian province may be regarded as the headquarters of the 

 group. 



Remains of Rodents have been found, ia the fossil state, 

 as far back as tlie eocene formation. 



II. The Insectivoea.— It is exceedingly difficiilt to give 

 an absolute definition of this group of mammals. But all 

 the Insectivora possess more than two incisors in the man- 

 dible ; and their molar teeth, which are always coated with 

 enamel, have tuberculated crowns, and form roots. 



The fore limbs have the structure usual among ungui- 

 culate mammals ; and, in both limbs, the digits are provided 

 with claws. The hallux is not opposable, and, like the 

 other digits, it is provided with a claw. 



In addition to these distinctive characters there are 

 others which are met with in all members of the group. 



The Insectivora are, almost aU, either plantigrade or semi- 

 plantigrade. The clavicles are completely developed in all, 

 except Potamogale. The stomach is simple. The testes 

 of the male are either inguinal or abdominal, and do not 

 descend into a scrotum. The female has a two-horned 

 uterus. 



The cerebral hemispheres leave the cerebellum uncovered, 

 in the upper view of the brain ; and are almost, or wholly, 

 devoid of sulci and gyri. The corpus callosum is sometimes 

 exceedingly short. 



No Insectivore attains a large size, and some, such as the 

 Shrew Mice, are the smallest of the Mammalia. 



The Insectivora present a great diversity of organization, 

 the common Hedgehog being an almost central form. The 

 Shrews tend towards the Bodentia, the Tupayce towards 

 the Lemurs; while the Moles, on the one hand, and the 

 Galeopitheci on the other, are aberrant modifications. Re- 

 lations of a more general character connect them with the 

 Carnivora and the Ungulata. 



The Hedgehog {Erinaceus EtiropcBus) is pentadactyle and 

 plantigrade. It has a long flexible snout. The eyes are 

 small ; the pinnse of the ears are rounded, and the integu- 

 ment lining the concha is produced into a transverse, shelf- 



