THE FAMILIES AND GENERA OF BATS. 21 



1 no i _ o _ A - I Q Nyctincmvus brasiliensis, with corresponding 



part of permanent formula the same as in Lasiurus, it also appears to 

 be present, though I have been unable to verify the occurrence of mi 3 . 



A slightly reduced formula 1 „ _' ' 9 =20, appears to be charac- 

 teristic of the Desmodontida? and Phyllostomidse, though the pos- 

 terior tooth both above and below is ^occasionally so small that its 

 presence can not be positively determined. In Desmodus the doubtful 

 tooth is mp z , while in Phyllostomus it is mp 2 . In two specimens of 

 Artibeus (Nos. 38309 and 38310, U. S. Nat. Mus., Old Providence 

 Island, Carribbean Sea), on the other hand, I can find no trace of 

 mp j. For the Megachiroptera the complete milk dentition is prob- 

 ably the same as that of the Phyllostomidee. At least, I have verified 



- 2 3. 1. 1 2 

 the formula ..— k — '-.'-. =^0 in Cynopterus and Pterocyon. In both 



of these the posterior tooth above and below corresponds with pm *, 

 and pm 4 , respectively, pm 3 and pm s being conspicuously without a 

 preceding functional deciduous tooth. 



In form the. milk teeth are for the most part quite unlike those of 

 the permanent dentition. They are usually 

 slender, minute spicules, with straight or re- 

 curved tips, and their only function is prob- 

 ably, as has been frequently suggested, to aid 

 the young in clinging to the mother during 

 flight. In size they are so insignificant that 

 one may not infrequently persist in the edge of 

 an alveolus until the permanent tooth is nearly 



r _, ,. .,. P i e ' Fie. 1.— Milk dentition of 



grown, lhese peculiarities ot size and form, cynopteeus minutus, nias 

 together with the very early development of island, no. 141271. x 

 the permanent dentition, preclude all possi- 

 bility that the milk teeth can "be used in mastication, and indicate 

 that, whatever may be the case with other mammals, in bats the de- 

 cidous teeth can have had little if any influence on the modifications 

 of the permanent set. 



The simplest form of milk tooth is a straight terete spicule, tapering 

 to a sharp point, and with no evident differentiation between root and 

 crown. This is found in the lower cheek teeth of Cynopterus. The 

 next and more usual type differs in the definite recurving of the point. 

 This curve may be slight and gradual (canines and cheek teeth of 

 Cynopterus (fig. 1) and Pterocyon, "upper canine of Myotis yuman- 

 ensis) or strong and abrupt, sometimes almost angular (canines and 

 cheek teeth of Phyllostomidse, canines and incisors of Nyctinomus 

 brasiliensis) . Occasionally this type is further modified by a slight 

 but evident shortening and thickening of the crown, or the faint indi- 



