METHODS — PAL^ONTOLOGICAL 43 



cumstances as well. The bones of the same individual differ 

 very materially in early youth, maturity and old age ; so long 

 as the animal lives, its bones are perpetually changing, slowly 

 it is true, but with ready response to needs. Not only that, 

 but dislocated bones may and frequently do develop entirely 

 new joints, and their internal structure is remodelled to meet 

 the requirements of stresses differing in character or direction 

 from those of normal, uninjured bones. The general form 

 and proportions of any. mammal are determined chiefly by 

 its muscular system and this may be directly and confidently 

 inferred from its skeleton, for the muscles which are of im- 

 portance in this connection are attached to the bones and leave 

 their indelible and unmistakable mark upon them. In any 

 good text-book of anatomy this extremely intimate relation 

 of bone and muscle is made clear ; and it is shown how each 

 attachment of muscle, tendon and ligament is plainly indicated 

 by rough Unes, ridges, projections or depressions, which speak 

 a language intelligible enough to those who have learned to 

 interpret it. Given the skeleton, it is no very difficult 

 task to reconstruct the muscular system in sufficient detail. 

 Further, the teeth afford valuable information as to the food, 

 habits and appearance of the animal, for the bulk of the viscera, 

 a significant element in the general form, is principally con- 

 ditioned by the character of the diet. 



Beasts of prey, which live by catching and devouring other 

 animals, have a certain hkeness to one another, even though 

 they are in no wise related, except as all mammals are. The 

 Thylacine, or so-called "Tasmanian Wolf" (Thylacynus 

 cynocephalus) , a marsupial and related to the opossums, is 

 deceptively Uke the true wolves in appearance, although be- 

 longing to an order (MarsupiaUa) almost as widely separated 

 from that to which the wolves belong (Carnivora) as two 

 mammaUan groups well can be. This resemblance is as clearly 

 indicated by the skeletons as by the living animals themselves, 

 though the fundamental differences of structure which dis- 



