uf the Common Mole. 379 



The author believes that if this test were applied to the Cape 

 mole {Chrysochloins aurea), the teeth that Prof. Owen has pro- 

 nounced to be molars would be found to belong (some of them) 

 to the premolar series, and the huge biting-teeth in the anterior 

 part of the jaw to the incisor or premaxillary teeth. 



At the period when the young mole is about four inches long 

 the deciduous teeth are so far developed that most of them are 

 cutting their way through the gums, and all of them in a for- 

 ward state. The two premaxillary bones are separated by a 

 distinct suture from the maxillary, and by an extensive fissure 

 from the palatal plates, which they approach only in the median 

 line, by long projecting bony processes, and at the alveolar walls. 

 In these bones are planted the eight anterior (four in each bone) 

 of the deciduous teeth; these consist of slightly curved cylin- 

 drical tubes differing somewhat in the form of their crowns, that 

 of the posterior being pointed and larger than the others. This 

 tooth is implanted within the limits of the premaxillary bone, 

 the suture separating it from the maxillary passing through the 

 posterior portion of its alveolus, in which, in progress of deve- 

 lopment, is the large pointed crown of the first permanent 

 double-fanged tooth, which we can now positively assert to be 

 the homologue of the true canine, the peculiar implantation of 

 which. must therefore be described as a variation from the nor- 

 mal type to meet the requirements of a large and powerful 

 tooth implanted in a jaw insufficiently deep to receive a corre- 

 sponding fang. 



The next series of deciduous teeth are situated in the maxil- 

 lary bones ; these represent the deciduous premolars (commonly 

 called deciduous molars, and are succeeded by the permanent 

 premolars. 



In the lower jaw the canine tooth of the deciduous set may 

 be determined by its position and form viewed in relation to that 

 of the upper jaw ; but all the deciduous teeth of the lower jaw 

 are small and single-fanged, though the last or fourth deciduous 

 premolar has a tendency to develope itself into two fangs at the 

 extremity. 



The entire series of the deciduous set may therefore be ex- 

 pressed by the following formula — as 



Decid. Premax. or Incisor |, d.Q>.\, d. P.M. ^ x 2 = 32 ; 

 and that of the permanent set as 



Premax. or Inc. 'g, C. }, P.M.I, M. | x 2 = 44. 



Thus by actual observation the author has been enabjed to 



28* 



