THE MOLARS. 



625 



(c) Total length from above to below, measured through the centre : 



Inferior. Superior. 



1st 0.020 m. 0.027 m. 



2d 0.021 m. 0.021 m. 



3d 0.026 m. 0.026 m. 



(d) Length of the roots : 



Inferior molars 0.012 to 0.015 m. 



Superior molars 0.010 to 0.013 m. 



FIG. 295. 



A. Transverse section of the inferior jaw, showing the third molar of the first dentition and 

 its replacing one, with the relations which they affect in the alveolus at the moment of eruption. 



B. Third inferior molar of the second dentition covered by its milk-tooth. 



The free part of the molars, in proportion as the animal advances in age, 

 diminishes in length until finally it becomes a small shell or plate which is 

 moulded exactly upon the extremity of the replacing tooth ; the latter is thus, 

 as it were, crowned. The deciduous molars are always expelled regularly at 

 the period of eruption of the permanent molars. 



B. Molars of the Second Dentition. 



The permanent molars, twenty-four in number (twelve in each jaw and 

 six on each side), are designated numerically, proceeding from before to behind, 

 under the names first, second, etc. The first three, called premolars, always suc- 



40 



