SIGNIFICANCE OF PREHALLUX AND PREPOLLEX. 37 



that, though an accessory phalanx may occasionally occur 

 in the thumb, the number of phalanges in the fingers, on the 

 whole, is remarkably constant. "^ 



Later, in the course of evolution, the true first meta- 

 carpal and metatarsal became disj)laced and subsequently 

 disappeared in the great majority of Tetrapoda. Its occur- 

 rence in the Amphibia is therefore correlated "with the lowly 

 position of the group, while its appearance in animals such 

 as TaJpa and Pedetes may either be due to persistence or 

 atavism. The multiple condition of the Anuran prehallux we 

 regard as the result of fragmentation consequent upon the 

 degeneracy of the structure and the mobility of the pes. 



RECAPITULATION. 



After examining the available literature, and from a 

 consideration of the material investigated, we summarise as 

 folloA^'s : — 



(a) The first metacarpal and metatarsal of the manus 

 and pes are serially homologous with phalanges. 



(6) In spite of the fact that the epiphj'seal argument 

 in favour of the phalangeal nature of the first meta- 

 carpal and metatarsal loses weight on account of 

 the normal presence of distal and j^roxiimil epiphyses 

 to these bones in certain animals, e.g. Koala, we 

 consider sufficient evidence still remains to regard 

 the first metacarpal and metatarsal as phalanges. 



(c) Heptadactyly and hexadactj^y, which probably may 

 have occurred in the earliest Tetrapoda, cannot be 

 regarded at present as more than philosophical 

 speculations ; pentadactyly appears to be firmly 

 established throughout the kno\Mi Tetrapoda, both 

 living and extinct. 



(a) The prepollex and prehallux are regarded by the 

 authors as representing the missing first meta- 

 carpal and metatarsal respectively. 



" ACKNOWLEDGMENTS. 



In conclusion, we desire to exj)ress our indebtedness to 

 Professor R. Berry, University of Melbourne, for his 

 sympathetic interest and advice ; also to Mr. H. A. Longman, 

 F.L.S., Director of the Queensland Museum, for the use of 

 valuable material ; and to Mr. W. M. Tanner, Brisbane, who 

 generously undertook the preparation of the X-ray photo- 

 graphs used in this investigation. 



