MAMMALS IN GENERAL 9 



to mammal in comprehensiveness and accuracy is the word 

 " beast," derived through Norman-French from Latin ; but 

 this is somewhat marred by its use as a term of opprobrium 

 among children or its restriction by the agriculturist to horned 

 cattle. Consequently we are obliged to adopt " mammal " 

 as the most correct designation in English for the air- 

 breathing, warm-blooded vertebrates which suckle their newly- 

 born young. 



Before beginning a description of British mammals, living 

 or recently extinct, it might assist the unenlightened reader if 

 the author attempted a brief definition of the leading character- 

 istics of the Mammalia as a class. They are warm-blooded, 

 air-breathing vertebrates with a four-chambered heart, with a 

 skin covered usually with hair, wholly or partially ; possessing 

 differentiated teeth ^ ; lungs freely suspended in the cavity of 

 the chest (partitioned off^ by a muscular wall from the stomach) ; 

 red blood corpuscles without a nucleus ; and with glands in the 

 skin (usually on the under part of the body) especially developed 

 in the female for the creation of milk as nourishment for the 

 new-born young. They are also marked off^ from other verte- 

 brates—such as fishes, reptiles, and birds — by the exclusive 

 possession " of an outer ear (that is to say, a conch, or flap of 

 skin, muscle, and tendon, which focusses the vibrations of sound 

 on the inner hearing organ) ; by a heart which has only one 

 aortic arch on the left-hand side (not two arches as in reptiles, 

 or one on the right-hand side as in birds) ; by the existence 

 of four optic lobes in the brain for the organs of sight; by a 

 lower jaw of a more fused character, with peculiarities as to its 



^ That is to say, teeth not all of one pattern, as in the generality of reptiles, 

 most fishes, and primitive birds, but divided normally into four kinds : 

 incisors for seizing, canine teeth for tearing, premolars for champing, and 

 molars for grinding. 



2 The lowest known forms of the Mammalia, the existing Monotremes of 

 Australia, possess no conch, or external ear, but in all other Mammalia where 

 the conch is not present (as in the whales, certain seals, edentates, and 

 insectivores), there is every reason to believe them to be descended from 

 forms possessing the external ear. 



