X INTEODTTCTIOIf. 



genera as Noctilio, Cheiromeles, Molossus, and Mystaaina, in which 

 they are deeply united together, as in the allied family Phyllosto- 

 ■midcs. In aU the genera of the latter family (except Monophyllus, 

 Ischnocflossa, Phyllonycteris, Lonchoglossa, and Glossonycteris, of the 

 group Olossophagce) the premaxillaries are well developed and united 

 in the centre (Plate XXIV. figs. 2, 6), reaching their culminating 

 point in the sanguiyorous group Desmodontes, where they support a 

 pair of enormous trenchant incisors (Plate XXX. fig. 7 b). 



Zygomatic arches are well developed in Pteropodidce (Plate IV. 

 fig. 1) and Ehinolophidce ; in the latter family they reach their 

 greatest size in Trimnops * ; in Emballonuridce and Phyllostomidce 

 they are slender, and in several genera of the latter family {Carollia, 

 Phyllonycteris, Glossonycteris, and CJioeronycteris) wanting. The 

 depth of the sagittal and occipital crests varies much in different 

 species, even in those of the same genus, and evidently depends 

 chiefly on the size of the muscles of mastication, which have their 

 origin from the sides of the skull, the development of these muscles 

 again depending on the nature of the food of the animal with which 

 the form and size of the teeth are correlated. Thus in Besmodus 

 rufus, which lives on the blood of animals, and in which the grind- 

 ing-teeth are rudimentary, the crown of the skuU is quite smooth, 

 without trace of either occipital or sagittal crests. 



In the Megachiroptera the bony palate is broad behind, produced 

 behind the last molars, and gradually narrowing backwards (Plate IV. 

 fig. 6) ; in Microchiroptera it is abruptly narrowed in a line with 

 the last molars, and produced backwards, forming the floor of the 

 posterior nares (Plate XIV. fig. 5 a, Plate XXIV. fig. 3) ; or in some 

 genera of Phyllostomidce (Stenoderma, Pygoderma, Ametrida) the 

 horizontal plates of the palate-bones are partially or wholly deficient, 

 and the palate is deeply cut as far forwards, in some species, as a 

 line drawn between the first upper molars (Plate XXVIII. figs. 2-4). 

 The two species included in the group Furice have been placed in 

 separate genera, chiefly on account of the different development of 

 the horizontal plate of the palate-bones, although othervnse very 

 closely aUied (see pp. 356, 357), so that it is doubtful how far this 

 difference in structure can be regarded as a generic character. 



The auditory bullce ossea vary considerably in. the different species 

 in size, which appears to be correlated with that of the external 

 ear, though exceptions to this rule are not wanting, as, for instance, 



* See my paper " On Osteology of Tricetiops persicus," and plate, referred to 

 above, footnote, p. rii. 



