KINETOGENESIS. 275 



4. KINETOGENESIS IN THE VERTEBRATA. 



I have already adduced the evidence in support of 

 the doctrine that the structures of the hard parts of 

 invertebrates have been produced by muscular move- 

 ments. In turning to the Vertebrata we shall find that 

 the evidence indicating that the details of their hard 

 parts have had a similar origin, is quite convincing. 

 This branch of the animal kingdom presents two dis- 

 tinct advantages for this study. First, we have a more 

 complete paleontologic series than in any other. Sec- 

 ond, we have the best opportunity for observation and 

 experiment on their growth processes, since we our- 

 selves, and our companions of the domesticated ani- 

 mals, belong to this branch of the animal kingdom. 



I shall show first, the conditions under which ab- 

 normal articulations of the skeleton have been formed ; 

 and then the process involved in the formation of 

 normal articulations. I shall then apply these facts 

 to the phylogeny of the Mammalia as we know it, and 

 then in a more general way to the Vertebrata as a 

 whole. 



1. KINETOGENESIS OF OSSEOUS TISSUE. 



a. Abnormal Articulations. 



Hiitter, from whom I have quoted under the head 

 of " Kinetogenesis of Muscle," thus describes the effect 

 of abnormal conditions of joints on the articular sur- 

 faces of the bones which form them. He says: "We 

 have abundant opportunity to investigate the change 

 of condition which the joints undergo during a year of 

 fixed muscular contraction. 



''The ligaments and bursae undergo similar changes 



