BATS. 431 



from those in the fang in the minor degree of secondary undula- 

 tion ; being, in fact, much straighter than the coronal tubuli of the 

 human tooth, which they rather exceed in size at their origin : they 

 diminish more rapidly in size as they approach the enamel, and give 

 off more numerous and conspicuous lateral branches ;(1) presenting a 

 stellate appearance in transverse or oblique section. The median 

 tubuli rise vertically to the summit of the crown, the lateral ones 

 diverge with a graceful curve convex towards the summit ; at the 

 neck of the tooth they rather abruptly take the opposite curvature, 

 still proceeding transversely outwards ; but gradually incline down- 

 wards as they approach the ends of the fangs. (2) In the thick cement 

 at this part of the molar teeth a few of the cells assume the angular 

 form, and approach the size of the ordinary Purkingian cells ; in the 

 rest of the fang the clear cement is studded with more minute and 

 simple opake cells. 



The boundaries of the dentinal cells, (3) which were scarcely dis- 

 cernable in the canine tooth, are very conspicuous in the molars, 

 especially near the periphery of the crown. They are of unusually 

 large size in proportion to the whole tooth, being absolutely larger 

 than the dentinal cells of the human tooth, and their interspaces 

 dilate here and there into semi-opake streaks. In vertical sections 

 of the molar teeth the part of the boundary of the cells next the 

 periphery of the crown was most conspicuous, forming a semi- 

 circular line, clear or opake, according to the focus, convex towards 

 the periphery, arching across from ten to twelve of the dentinal tubuli : 

 the whole producing the appearance of an imbricated structure. In 

 transverse sections the whole contour of the dentinal cells is visible : (4) 

 they are irregular in form and size as seen in a section exposing 

 them on the same plane, where they are probably cut through at 

 different levels, some of the largest present an irregular hexagonal 

 figure, and a diameter of g^th of an inch. 



The enamel of the teeth of the Pteropus is unusually opake, 



(1) PI. 113, fig. 2, d. (2) lb. fig. 1. 



(3) lb. fig. 1, and PI. 113 a, fig. 2, d', d},, 



(4) PI. 113 a, fig. 1. 



