380 Mr. C. Spence Bate on the Dentition of the Common Mole, 



support the correctness of Prof. Owen's inductive analysis of the 

 teeth of the mole, and demonstrate the homological relation of 

 the several teeth. 



At the period of examination no fur was developed upon the 

 young mole's skin. The deciduous teeth had not yet pierced the 

 gum, whilst the small extent of fang yet to be produced at the 

 extremity shows how nearly the period had arrived for their pro- 

 trusion through the gums j yet we cannot but be struck with the 

 feeble connexion existing between the teeth and the alveolar walls, 

 which rather appear to be undergoing absorption and waste for 

 the purpose of the reception of the permanent set, than to be 

 strengthening to support the milk-teeth in any efficient action. 

 These circumstances, together with the forward stage of the 

 development of the permanent set, suggest the idea that the 

 deciduous teeth are developed according to a law of growth, but 

 are not required to fulfil any want in the economy of the young 

 animal's life ; for they can scarcely be developed in their places 

 before the period of the eruption of the permanent teeth; and 

 this is probably coeval with the time when the fur is placed 

 upon the young creature's back, and it is able to excavate the 

 soil for itself. 



Large spaces separate the deciduous teeth from each other, 

 which, together with the feeble attachment that they have to 

 the jaw, shows them to be useless as organs of mastication : 

 this is most distinctly exhibited in the character of the deci- 

 duous premolars when compared with that of their permanent 

 successors. 



It is the most usual condition in the Mammalia above the 

 Cetaceans and Bruta for the deciduous teeth that anticipate the 

 premolars to be developed upon a more complex type, assuming 

 more nearly the shape of the true molars than do those of the 

 permanent set ; but the author believes that this is but a rule 

 subservient to a universal law — that whenever teeth are deve- 

 loped according to a law of growth, and not required for any 

 functional purpose, they have a tendency to return to the primi- 

 tive form of the Mammalian type ; and such he takes to be the 

 character of the deciduous teeth of the genus Talpa. 



The author also described the microscopic structure of the 

 teeth, and exhibited numerous drawings of the minute anatomy 

 both of the teeth and jaws of the animal. 



EXPLANATION OF PLATE XL 



Fig.\. Upper jaw; adult. Fig. 3. Lower jaw; adult. 



Fig. 2. Ditto; immature. Fig. 4. Ditto; immature. 



1, 2, 3 luc., incisor or premaxillary teeth. 



1, 2, 3 d. Inc., deciduous incisor or premaxillary teeth. 



