CHAPTER IV 



THE SKELETON AND TEETH OP MAMMALS 



With very rare exceptions, and those only of the latest 

 geological period (Quaternary), the fossil remains of mammals 

 consist only of bones and teeth. The evolutionary changes, 

 so far as these are preserved, are recorded therefore in terms of 

 dental and skeletal modifications. To render these changes 

 intelligible, it is necessary to give some account of the mam- 

 maUan skeleton and teeth, with no more use of technical 

 language than is unavoidable; ordinary speech does not 

 furnish a sufficient number of terms, "nor are most of these 

 sufficiently precise. With the aid of the figures, the reader 

 may easily gain a knowledge of the skeleton which is quite 

 adequate for the discussion of fossil series, which will follow 

 in the subsequent chapters. 



I. The Skeleton 



I. The most obvious distinction of the skeletal parts is 

 into axial and appendicular portions, the former comprising 

 the skull, backbone or vertebral column, ribs and breastbone 

 or sternum, and the latter including the hmb-girdles, limbs 

 and feet. In the axial skeleton only the ribs and certain bones 

 of the skull are paired, but in the appendicular all the bones 

 are in pairs, for the right and left sides respectively. 



The skull is a highly complex structure, made up of many 

 parts, most of which are immovably fixed together, and per- 

 forming many functions of supreme importance. In the first 

 place, it affords secure lodgement and protection for the brain 

 and higher organs of sense, those of smell, sight and hearing, 



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