THE INSECTIYORA. 376 



tine nearly a foot from the p^'lorus, and far distant from the 

 biliary duct. 



There are tvfo anterior cav£e; and the external jugular 

 vein is very much larger than the internal. 



In the male, the inguinal canal remains permanently open, 

 and there is a large uterus masculinus. In the female, the 

 uteri are quite separate, and each opens by a distinct os tincce 

 into the vagina. 



The distribution of the Jiodentia is almost world-wide, 

 Madagascar being the only considerable island in which indi- 

 genous Rodents are unknown. The Austro-Columbian prov- 

 ince may be regarded as the headquarters of the group. 



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

 as far back as the eocene formation. 



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

 an absolute definition of this group of Mammals. But all the 

 Jnsectivora jDOSsess more than two incisors in the mandible ; 

 and their molar teeth, which are always coated with enamel, 

 have tuberculated crowns, and form roots. 



The fore-limbs have the structure usual amono; un2:ui- 

 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 liisectivora are, almost all, 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 3iamr}ialia. 



The Insectivora present a great diversity of organization, 

 the common Hedgehog being an almost central form. The 

 Shrews tend toward the Hodentia^ the Tupayoe toward the 

 Jjeinurs; while the Moles, on the one hand, and the Galeo- 

 pithed on the other, are aberrant modifications. Relations of 

 a more general character connect them with the Carnivora 

 and the Ungulata, 



