INTELLECT 



ing therefore a less specialised uimdition of the limbs. It is 

 au interesting fact that the angulation of the limbs is to some 

 extent obliterated in very bulky creatures, and almost entirely 

 so in the elephants (see p. 217), which seem to need strong and 

 straight pillars for the due support of their huge Ijodies. 



The alertness and general intellectual superiority of mammals 

 to aU animals lying below them in the series (with the exception 

 of the birds, which are in their way almost on a level with the 

 ilammalia) are seen by their active and continuous movements. 

 The lengthy periods of absolute motionlessness, so familiar to 

 everybody in such a creature as the Crocodile, are unknown among 

 the more typical Mauunalia except indeed during sleep. This 

 mental condition is clearly shown by the proportionate develop- 

 ment of the external parts of all the organs of the higher senses. 

 The Mammalia as a rule have well-developed, often extremely 

 large, flaps of skin surrounding the entrance to the organ of 

 hearing, often called " ears," but Ijetter termed " pinnae." These 

 are provided with special muscles, and can be often moved and 

 in many directions. The nose is always, or nearly always, very 

 conspicuous by its naked character ; by the large surface, often 

 moist, which surrounds the nostrils ; and again by the muscles, 

 which enable this tract of the integument to be moved at will. 

 The eyes, perhaps, are less marked in their predominance over the 

 eyes of lower Vertebrates than are the ears and nose ; but they 

 are provided as a rule with upper and lower eyelids, as well as 

 liy a nictitating membrane as in lower Vertebrates. The apparent 

 predominance of the senses of smell and hearing over that of 

 sight appears to be marked in the Mammalia, and may account 

 for their diversity of voice as well as of odour, and for the 

 general sameness of coloration which distinguishes this group 

 from the brilliantly-coloured birds and reptiles. The head, too, 

 which bears these organs of special sense, is more obviously 

 marked out from the neck and body than is the case with the 

 duller creatures occupying the lower branches of the ^^ertebrate 

 stem. 



The Hair. — The Mammalia are absolutely distinguished from 

 all other Vertebrates (or, for the matter of that, Invertebrates) 

 liy the possession of hair. To define a mammal as a Vertebrate 

 with hair would be an entirely exclusive definition ; even in the 

 smooth Whales a few hairs at least are present, which may be 



