24G i\Ir. K. Andersen on the Bats 



fossa, a projecting of the hinder part of the zygomatic arches, 

 making the zygomatic width of the skull considerably larger 

 than the mastoid width (fig. 2 a). 



In the pMIipphiensis section the base of the sella forms, 

 together ivith the wtemasaJ lobes, a cup-like expansion. In 

 the trifol'iatas section the internasal lobes are quite, or 

 almost quite, normal, the lateral expansions confined to the 

 sella and wing-like, giving the sella some resemblance to 

 a Trifolium leaf (hence the name " trifoliatus ") or a Maltese 

 cross. 



In the jihUippinensis section the wing-structure ^ is very 

 primitive, quite as in other primitive species of the genus 

 {meffnphyllifs, borneensis, minor, and many others) : the 

 f mirth metacarpal slightly longer than the fifth and the third ; 

 IV.2 1 and V.^ but slightly longer than IV.^ and W In 

 the trifoliatus section the wing-structure is considerably 

 modified : — the third metacarpal is much shortened, the fourth 

 slightly lengthened, the fifth more so, making as a final 

 result the fifth metacarpal decidedly the longest of all, and 

 very much longer than the third (supposing the length of 

 the forearm, in all species of the group, to be exactly 

 1000 mm., the fifth metacarpal, in the trifoliatus section, is 

 no less than 133 mm. longer than the third, in jj hi lippiyiens is 

 and achilles 18 mm. only) %. At the same time the first 

 phalanx of the third finger, in the trifoliatus section, is much 

 leugthened, chiefly by a removing, iyi proximal direction, of 

 the joint between the metacarpal and the first phalanx; in 

 other words, the piece by which the third metacarpal has 

 been shortened has been added to the length of the first 

 phalanx of the same finger. Thirdly, III.-, IV.-, and V.^, 

 in the trifoliatus section, are considerably lengthened. 



The mechanical reason for this modification of the wing 

 is, probably, the following : — A lengthening of the distal 

 phalanges gives a broader wing, consequently an increased 

 power of flight ; the third finger, as being the longest of all 

 and the nearest to the front margin of the wing (when 

 expanded), has to sustain the heaviest pressure of the air; 



* The remarks ou tlie wiug-stmcture to be compared, point for point, 

 with the diagram on p. 247 and tlie wing-indices on p. 257. 



t For brevity's sake I call the distal phalanges of the 3rd, 4th, and 5th 

 fino^ers III.^, IV.^. andV.^, the proximal phalanges of the same fingers 

 m.\ IV.i, and \.\ 



X An almost exact parallel to this modificatiuu of the wmg-structure 

 is seen in Rh. ferrum-eqidmim compared with the primitive forms of 

 the group to which that species belongs (f. i. lih. megapliyllus, borneensis, 

 kc). 



