THE BATS 



(CHIROPTERA). 



Distinguished by the possession of wings formed by a membrane attached to the body, and commonly also to the 

 hind-limbs and tail, and capable of being extended by the remarkably elongated digits of the fore-limbs; 

 complete dentition; two pectoral mammae; discoidal placenta. 



The body in the bats is in general thick- 

 set and compact, the neck short, the skull 

 rather small than large, somewhat elongated. 

 Owing to the remarkable development of 

 various appendages of the skin, however, 

 as well as to the broad muzzle, the head 

 in the living animal appears to be rather 

 large. The eyes depart from the general 

 rule for nocturnal animals in being rather 

 small, sometimes even very small; the ears 

 are always large, often peculiarly devel- 

 oped; the nose is sometimes naked, and 

 situated at the end of the snout, sometimes 

 adorned in a singular manner with flaps of 

 skin supported by cartilage. 



The brain -case is mostly rounded, and 

 frequently divided from the facial region by 

 a marked constriction. The orbit is mostly 

 continuous with the temporal fossa or de- 

 pression at the temple, and it is only rarely 

 bounded by a narrow external bony ring. 

 The structure of the premaxilla is often very 

 peculiar. Only in rare cases do the two pre- 

 maxillary bones meet in the middle; for the 

 most part they are separated by a wide in- 

 terval, so that the upper incisors are placed 

 quite to the side, and often they are reduced 

 to small bony scales which scarcely cut the 

 gums. 



The dentition belongs to the insectivorous 



type, and even that of the flying-foxes, which 

 we leave out of account in the meantime, can 

 be derived therefrom. All the other bats 

 may, without hesitation, be designated as 

 flying Insectivora. 



The number of the teeth varies in an ex- 

 traordinary manner, from 24 to 38 for the 

 total, but the numbers 32, 34, and 30 are 

 those by which the total is most frequently 

 represented. Twenty-three of the sixty-seven 

 genera that have been distinguished, that is, 

 more than one-third of the whole, have 32 

 teeth. Besides the original deviations, espe- 

 cially in the number of the molars, the dis- 

 tinctions chiefly depend upon this, that in 

 many genera many incisors and premolars 

 drop out very early, or are not replaced at 

 the change of teeth. The incisors are mostly 

 very small, in the upper jaw placed, as we 

 have seen, to the side, and there also pecu- 

 liarly apt to disappear. The canines, which 

 are always present, are large, recurved, and 

 provided with cutting edges, in many genera, 

 as notably in the vampyres, very large and 

 prominent ; the premolars sharp and conical ; 

 the molars furnished with two or three pointed 

 cusps, which are so arranged as to fit closely 

 into one another, so that they do not get 

 ground away by use, but are kept always 

 sharp. The dentition is thus specially adapted 



