i6 INTRODUCTION 



This represents a very near approach to the typical complete 

 dentition of the higher mammals, from which it appears to have 

 receded, by the loss of one pair of upper incisors and of a pair 

 of premolars above and below. Further reduction is fore- 

 shadowed by the small size of the first two upper premolars, 

 especially the second upper, while the tendency is visible, 

 although less markedly so, in the second lower premolar. 

 Ascending the scale, we find Plecotus, having dropped a pair of 



upper premolars, with pm ^^ and a total of thirty-six teeth. 



In Pipistrellus, the next highest, a pair of lower premolars has 

 vanished (both remaining pairs being quite small), and the 



formula is ■bm ^ ~ ^, total thirty-four. Barbastella and Nyctalus 



^ 2-2 



have also a total of thirty-four, but in the latter the anterior 

 upper premolar has become rudimentary, and the corresponding 

 lower one is much reduced in size. In Vespertilio the former 

 tooth has entirely disappeared, reducing the total to thirty-two, 

 all of which are functional. In Rhinolophus the number is 



again thirty-two, but in this case the premolars are — — , with 



the anterior upper and central under often rudimentary : the 



incisors, ^ ~ ^ , differ in number and arrangement from those 



2 — 2 



of the vespertilionid bats ; the upper ones are quite minute and 

 functionless. 



The missing teeth required to complete the typical 

 mammalian dentition of forty-four have usually been taken as 

 upper incisor i and premolar i in both jaws, the next to dis- 

 appear being either premolar 2 or 3. Mr Oldfield Thomas 

 however, gives good ground for regarding the missing pre 

 molar as 2} The posterior molar of both jaws is reduced i 

 size, but it is present in all British species. 



The shape and form of the teeth will be best understood 

 by a reference to the diagrams representing the dentition of 

 each species. The premolars resemble the simple canines, but 

 are conspicuously smaller ; the last is always much the largest, 

 and is double rooted. 



' Ann. and Mag. Nat. Hist., April 1908, 346-348. 



in 



