ix ] DEVELOPMENT. 149 



of the cerebral cavity, is strikingly shown. At the same 

 time the alveolar borders of the jaws gradually enlarge to 

 adapt themselves to the increased size of the permanent 

 teeth which they have to support, and the various ridges and 

 tuberosities for the attachment of muscles become more 

 prominent 



During these changes a gradual consolidation takes place 

 in the structure of the skull generally, by the partial or com- 

 plete union of certain of the bones by synostosis. The 

 union of the different bones generally proceeds in a certain 

 definite order, which, however, varies much in different 

 species. Sometimes it extends so far as to lead to complete 

 obliteration of all the cranial sutures. 



