130 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



genus, of which some few species (e.;/. Ptcropus aneiteanus and 

 leucopterus, and Cynoptcrus) retain remnants of the ancient cuspi- 

 date structure, while others (e.g. Pteropus coronatus, . . .) have 

 lost all trace of molar cusps." Oldfield Thomas, Proc. Zool. Soc., 

 1888, pp. 474-475. 



In the treatises especially of Harrison Allen 1 and of Matschie 1 

 we have examples of the teeth of Cheiroptera studied respectively 





FIG. 82. Superior view of the right half of the lower jaw of a Microcheiropter, ArtH* us 

 pcrspicillatus, showing the progressive change in nij, r. 2 of a cuspidate into a "basin-shaped" 

 molar, x. After H. Allen. 



from the trituhercular standpoint and from the older standpoint in 

 which there was no especial attempt to establish tritubercular homo- 

 logies. The very interesting and important work of Matschie on 

 the Fruit Bats develops particularly the secondary formation from a 



A 



B 



hy. pr. 



Fid. 83. Progressive stages in the development of the hypocone in Microoheiroptera. A. Tri- 

 tubercular stage (Atalnpha cinerea). x i. B. Transitional stage (Promops perotis californicus). 

 X i. C. Quadritubercular stage with strongly-developed hypocone (Nyctinomus brasilicnsis). x |-. 

 After H. Allen. Possibly the series may be reversed, and we may be witnessing in the stages 

 C, B, A, the secondary loss of the hypocone, caused by the shortening of the skull and 

 tooth row. 



tritubercular crown of a basin-shaped crown with a depressed centre 

 and a rim surmounted with irregular cusps, analogous to that which 

 we find among the most primitive Multituberculates. If all the 



1 See titles under "Special References." 



