XVlll GENERAL CHARACTERS. 



iVotop<<?Hs, typical Microehiroptera), number of free caudal vertebrae 

 probably at least ten *. 



Tbe characters in wbich living Megachiroptera differ from the 

 above scheme of the ancestral form may be divided into two classes, 

 those that have become j^.recZ, i.e. firmly and invariably established 

 in all living genera, and those that are plastic, i. e. subject to 

 variation from genus to genus. 



The modifications common to all living members of the Suborder 

 are these : — 



(1) The bony palate is elongated behind the tooth-rows and the 

 zygomatic process of the maxillary bone (the practically complete 

 absence of the postdental portion of the palate in a single genus, 

 Casinyrteris, is without doubt a secondary modification, Casinycteris 

 being closely related to a form (S colony cter is) with normal Mega- 

 chiropteran palate) : 



(2) Postorbital processes are developed : 



(3) The molar structure is modified from the common Insecti- 

 vorous type into the ordinary Megachiropteran type as follows 



i~^ 4*5 



Fig. I. — Typical rnolar structure of Megachiroptera compared with 



that of Insectivora. 



A. right upper m^, B. left lower m^ oC Talpa eiiropma (B.M. 8.7.7.4). 



A', right upper m', B'. left lower mi o{ Rauseitus (egyptiacus (B.M. 64.8.17.45). 



A and B f , A' and B' f. ' 



For explauation of nuiiibering of cusps see footnote t below. 



(fig. I.): in the upper molariform teeth cusps 1, 2, and 3t have 

 disappeared, cusp 4 and the reduced cusp 5 form together a longi- 

 tudinal ridge along the outer side of the teeth, cusps 6 and 7 



* Most of the characters enumerated above have already been suggested by 

 Herluf Winge in his " Jordfundne og nulevende Flagermus {Chiroptera) fra 

 Lagoa Santa, Minas Gei-aes, Brasilien ; med Udsigt over Flagermusenes 

 indbyrdes Slsegtskab" (E Museo Lundii, vol. ii. pt. i. p. 27; 1892). For a highly 

 instructive account of the modifications that have taken place in the develop- 

 ment of the Chiropteran type from some primitive form of Insectivora, see 

 pp. 18-23 of Winge's memoir. 



t The molar cusps are named in accordance with Herluf Winge's theory 

 (" Om Pattedyrenes Tandskifte, isfer med Hensyn til Tjendernes Former," 

 Vidensk. Meddel. naturhist. Foren. Kj0benhavn, for 1882, pp. 16-18, pi. iii.). 

 The three cusps, labial in the upper but lingual in the lower teeth, that form 

 the tips of tbe W of a typical Insectivorous molar are termed, in antero- 

 posterior direction, respectively 1, 2, and 3, cusp 2 being the oldest, homologous 

 with the single cusp of a Reptilian tooth; the two cusps forming the bases of 

 the W are named 4 and 5 ; and the "' heel " of the upper molars, when single, 

 cusp 6, when double, cusps 6 and 7. 



