XX PLASTIC CnARACTERS. 



jinteriorly, and tlio aberrations from this typical (Insectivorous- 

 like) sha[)e are, apart from Ilypsignatlms, but few and not very 

 peculiar. The rostrum is unusually deep (truncate) in front in 

 JSIeqarops and Nyctimene (both of the Cynoptevus section) ; in 

 Niictimene the medial portion of the nasals is produced forward 

 and downward as a triangular projection firmly united with the 

 anterior edge of the mesothmoid cartilage (evidently acting as a 

 support of the nasal tubes; c/. fig. 61, p. 684). In Fruit-bats 

 with weak dentition (narrow cheek-teeth) the rostrum is lower and 

 thinner than usual ; compare Stenonycteris (fig. 3, p. 49) with 

 llousettus (fig. 2, p. 17), Pteropus scapulatas (fig. 18, p. 404) with 

 the average Pteropus skull, Sphcprias (fig. 60, p. 672) with the 

 ordinary Cyaopterine type of skull (fig. 48, p. 588), and all Macro- 

 (/lossince, except the more heavily-toothed Eonycleris. The only 

 strikingly peculiar modification is seen in males of Hypsignathus 

 {fig. 33, p. 502) 4 the rostrum is greatly increased in size and 

 jjarticularl}' in depth, its dorsal and ventral profiles subparallel, its 

 lateral surfaces concave (a large subcutaneous air-sac is present on 

 either side of the rostrum), and a strong vertical crest runs from 

 the nasals to the alveolus of the canine (supporting a cutaneous fold 

 of the upper lip) ; in females of the same genus the rostrum is 

 somewhat similarly, but much less excessively, modified. 



2. Premaxillce. 



Vary in shape (breadth, degree of reduction), in direction, and 

 in the mode of interconnection of the alveolar branches. The 

 palatal branches of the premaxilliB are always absent. 



Breadth. — The three Macroglossine genera Mdonycteris, Ntso- 

 nycteris, and Notopteris exhibit what is probably the most primitive 

 form of the premaxilke : the ascending branch is unreduced in 

 breadth at its upper extremity, gradually narrowing interiorly, so 

 that the breadth of the bone near the alveolar margin is only 

 one-half or one-third of its breadth at the upper extremity (fig. 76, 

 p. 791). The next stage is shown by genera in which the ascending 

 branch is considerably reduced in breadth above, being quite or 

 nearly as narrow above as near the alveolar margin (ex. Pteropus 

 and allied genera ; Epumophorus ; Eonycttris ; Meijaloylossiis ; 

 Macroqlossus; &c.) ; a still higher degree of reduction by genera 

 in which the bone is tapering to a point above, its upper extremity 

 often slightly curved forward (ex. nearly all geneia of the Cyno- 

 pterus section) ; and finally, the whole of the ascending branch may 

 become so thin as to be almost linear throughout (Dohsonia). The 

 whole of the premaxillary region is increased in breadth in Bypsl- 

 (jnathus (owing to secondary modifications in the shape of tlie 

 rostrum). In Nyctimene (fig. 61, p. 684) the alveolar branches 

 are unusuall}' deep (vertically), the ascending branches so short as 

 not to reach the nasal bones (extremity of rostrum modified, for 

 support of the peculiar nasal tubes in this genus). 



Direction, — As a rule the ascending branches of the prcmaxillse are 



S4 



