348 On the Missinr/ Premolar of the Chiroptera. 



milk find permanent teeth. Now, with one exception, ex- 

 phtined below, no bat has ever been recorded as havin<^ more 

 than two milk-preniolars, those belonging to the two |)Osterior 

 teeth, the tritus and tetartus. The anterior Chiropteran 

 cheek-tooth therefore never changes, and is, ipso fucto^ /)' 

 (unless it is w^;', a possibility about which I cannot at 

 present express any opinion, though I do not think it 

 unlikely). 'J hat the absence of the milk-tooth cannot be 

 correlated with the reduction that the anterior permanent 

 tooth generally exhibits is shown by the fact that in Pterocyon 

 he/vus this premolar is decidedly larger than the incisors, 

 and yet no trace of a milk-tooth belonging to it is to be 

 found, while the milk-incisors are large and conspicuous. 



The one exception referred to is Leche's record of three 

 upper milk-premolars in Glossophaga*, although the adult has 

 only two j)crmanent premolars. But this latter fact gives 

 the clue to the apparent anomaly of the Glossopkaga dentition, 

 for to my mind it indicates without doubt that the anterior 

 cheek-tooth regarded by Leche as a milk-tooth is simply 

 the ordinary anterior premolar itself, somewhat premature in 

 development and deciduous in the adult. 



As I agree with Dr. Knud Andersen that it is the outer 

 and not the median upper incisor that has disappeared in 

 bats t, the following would be the full Chiropteran formula 

 when at its maximum : — 



ri 3 4 fl 2 3^1 

 ^ r " ' ' M. 1x2=22.38. 



3 4 



ll 3 4 ll 2 3. 



the teeth just mentioned are the non-changing protus and protid, while 

 the objects he labels as ;jm. I above and ind. 1 below are not teeth at all, 

 but soft structures which he has mistaken for such in the belief that teeth 

 ought to be found there. 



* I.unds Univ. Arsskr. xiv. p. 11, pi. ii. fig. vii. (1878). 



t Partly because of the reduction of the third lower incisor in many bats, 

 partly because of the way the lower canine bites on to the space where a 

 missing i^ would have stood, and partly on the analogy of such other mem- 

 bers of the Fera3 as Gmtetes, where this reduction can be clearly proved 

 (see P. Z. S. 1892, p. 504). Mr. Miller's argument (' Genera of Bats,' p. 27, 

 1907) .about the median imperfection of the premaxilhe appears to me 

 quite fallacious, for the innermost incisor of three, in one geological epoch, 

 would not be atiected by the fact that in a later one, aftei- the reduction 

 to two incisors, the premaxillte were (/om(/ to become imperfect in the 

 middle line of certain genera. The reduction from three to two must 

 have taken place long before any tendency to premaxillary imperfection 

 began to appear. 



