432 BATS. 



dark-coloured, and its fibrous structure ill defined. (1) In the canine 

 the fibres are ^ih inch in diameter ; they are directed at the sides 

 of the crown, almost perpendicularly to the surface of the dentine, 

 with a slight convex bend towards the summit of the tooth ; the 

 layers of growth proceed very obliquely from without, down- 

 wards and inwards ; I counted eleven layers in a transverse section 

 of the enamel at the middle of the crown of the canine. 



The succession of the teeth in the order of Volant Mammals 

 has received the most satisfactory elucidation from the careful and 

 minute researches of M. Rousseau on the Vespertilio murinus.{2) 

 The deciduous teeth make their appearance above the gum in Bats, 

 as in Shrews, before birth; but they attain a more completely 

 developed state, and are retained until a short time after birth, 

 when they are shed. The series consists of m. fE|, c. J^j, m. |=|,=22 : 

 magnified views of the deciduous teeth in situ of the common Bat 

 are given in PL 112, fig. l", and of both the deciduous and perma- 

 nent teeth detached on the right hand of figs. 1 and l". The 

 deciduous incisors (i) have slightly expanded tridentate crowns ; the 

 anterior and longest does not exceed xVth of an inch in length : the 

 lower deciduous incisors are shorter, but of a similar form. The 

 canines {c") very slightly exceed the incisors in length, but are a 

 little more deeply implanted, and the middle cusp of the tridentate 

 crown is longer and more conical. The upper deciduous molars (p') 

 resemble the incisors, but are broader in proportion to their length, 

 v>'hich scarcely equals one line ; the lower deciduous molars are 

 more slender. No tooth has been observed to precede the third 

 tooth of the permanent molar series, (p) which, by its shape should 

 be regarded as a premolar : if this tooth be classed, from the 

 circumstance of its not displacing any predecessor, amongst the 

 true molars, these will then be four in number on each side of 

 both jaws, as in the Marsupialia. 



In the foetus of a species of Pteropus so far advanced as to 



a) PI. 113, fig. 2, e. 



(2) " Memoire zoologique et anatomique sur La Chauve-souris commun, dite ' Murin,' '* 

 Magazin de Zoologie, 1839. 



