MAMMALS 475 



the chief orders of placentals, although some of them are present 

 only in the domesticated state ; one exception must in fact be 

 made to the generalisation given above about the success of 

 mammals, for they have not stood up well to the impact of 

 civilised man. The largest wild mammal which has maintained 

 itself in Britain without protection is the badger, of weight about 

 twenty-five pounds, and it is remarkable that two of the most 

 successful species, the brown rat and the rabbit, are human 

 importations which are not native to the country. The birds, 

 although they also have lost many of their larger species, have 

 suffered much less. Most of the more successful mammals are 

 small, unobtrusive and nocturnal, and survive, hke hedgehogs 

 in suburban gardens, largely because they are seldom seen. 



The orders of eutherian mammals are put into four main 

 groups, which may be called cohorts ; each cohort may be assunied 

 to be descended from what was, at the time when the placentals 

 were becoming established, a single order. The first of them is 

 the Unguiculata, or nailed animals, which have mostly retained 

 a primitive internal structure with many features reminiscent 

 of reptiles. Great Britain has examples of three orders, the 

 Insectivora, Cheiroptera, and Primates. 



INSECTIVORA 



There is no vernacular Enghsh name for the insectivores ; 

 their Latin name means ' insect-eating ', but it is important 

 to remember that ' insect ' here has the meaning which it has 

 for the populace, not that which it has for zoologists. An insecti- 

 vore may feed on insects, on other arthropods, on snails and 

 slugs, and on worms ; some, such as hedgehogs, also take small 

 vertebrates and some vegetable matter. 



There is no peculiarly insectivore character, but the order 

 is notable for possessing many features which are believed to 

 be primitive ; that is, features which are found in the earliest 

 fossil mammals, or in reptiles, or in both. The cranial cavity 

 is small, the tympanic bone is ring-shaped, and the palate is 

 fenestrated, that is, full of holes. The teeth are often what is 



considered to be the full set, with formula ^^, and the crowns 



of the cheek teeth have a small number of sharp-pointed cusps. 

 There is a clavicle and usually a centrale, and the radius and ulna 



