545 



a later period shows traces of a post-permanent downgrowth. Now 

 the lingual downgrowth giving rise to the successional tooth enlarges 

 in relation to the an tero- external cusp. 



This enlargement is at about the same stage of development as 

 the corresponding downgrowth in connection with dpm^. 



As the posterior end of the antero-external cusp is approached, 

 not only has this enlargement disappeared but the dental lamina does 

 not sink nearly so deeply into the substance of the jaw. From this 

 it must be concluded that the successor to the penultimate deciduous 

 premolar is developed in relation to the antero-external cusp of that 

 tooth. 



As the posterior end of the postero-external cusp is reached, the 

 dental lamina is seen still unenlarged and still shortened up, so to 

 speak; at the same time more deeply down in the jaw, lying to the 

 inner side of the penultimate dptn, the permanent carnassial is to be 

 seen in an advanced stage of development. If this tooth be examined 

 at a later stage a downgrowth of dental lamina may be seen on its 

 lingual side. I have not seen any labial downgrowth even at the 

 time of birth but I have not yet examined foetal pups. I am not 

 in a position to say definitely whether this tooth belongs to the true 

 permanent series, or whether, owing to its great development it may 

 not be a delayed milk tooth as my friend Mr. M. F. Woodwabd has 



>:i b 



Fig. 5. Section through last Deciduous Premolar of Dog (3 days old), upper Jaw. 

 a labial, b lingual Side. 



