784 PHYLUM CHORDATA : CLASS MAMMALIA 



bark of young trees ; it is gregarious and a burrower ; it is 

 very prolific, frequently breeding four times in a year. It 

 is said to live, in normal conditions, seven or eight 

 years. The rabbit seems to have had its original home in 

 the western Mediterranean region, but it has spread widely 

 throughout Europe, and is now abundant in regions, such 

 as the Highlands of Scotland, in which, a few generations 

 ago, it was rare. Introduced into Australia and New 

 Zealand, it has multiplied exceedingly, and has become a 

 scourge. There are many varieties of rabbit, some in 

 isolated regions perhaps illustrating the effect of segrega- 

 tion in fostering divergent types. But the varieties with 

 which we are familiar in the breeds of tame rabbits illus- 

 trate variation under domestication and the efficacy of 

 artificial selection. 



External appearance. — ^The head bears long external 

 ears, which are freely movable. The black patch at the 

 tip of the ears in the hare is either absent or very small in 

 the wild rabbit. This external ear is characteristic of most 

 Mammals, and collects the sound like an ear-trumpet. 

 In the rabbit it is longitudinally folded, thin and soft 

 towards its tip, firm and cartilaginous at its base. The eyes 

 have two eyelids with few eyelashes, and a third eyelid or 

 nictitating membrane — a white fold of skin — in the anterior 

 upper corner. This third eyelid, which also occurs in 

 Reptiles and Birds, is present in most Mammals, and is of 

 use in cleaning the cornea. It is absent in Cetaceans, where 

 the front of the eye is bathed by the water, and it is rudi- 

 mentary in man and monkeys, where its absence is com- 

 pensated for by the habitual winking of the upper eyelid. 

 The nostrils are two slits at the end of the snout, and are 

 connected with the mouth by a " hare-lip " cleft in the 

 middle of the upper lip. In front of the mouth are seen the 

 chisel-edged incisors, a pair on the mandibles, and two 

 pairs on the premaxillge — the smaller pair hidden behind 

 the larger pair. 'The first milk incisors above and below 

 never cut the gum, but are absorbed before birth ; the 

 second milk incisors above (there are none below) are 

 functional, but are shed about the third week of extra- 

 uterine life ; the same is true of the milk premolars. Into 

 the toothless gap or diastema between the front and back 



