SIGXIFICANCE OF PREHALLUX AND PREPOLLEX. 33 



THE PREPOLLEX AND PREHALLUX. 



These terms were given by Bardeleben, in 1885, to accessory 

 bones on the medial side of the carpus and tarsus respectively, 

 which either had previously been regarded as sesamoids or 

 were quite unknown ; the terms were first apphed to the 

 Mammalia, but it was subsequently shown that they also 

 occurred in the Reptiha and Amphibia. Bardeleben stated 

 (1889, p. 256) that these structures are found in certain members 

 of those orders of Mammalia provided with five functional 

 digits, viz., MarsupiaHa, Edentata, Rodentia, Insectivora, 

 Carnivora, and Primates. It is of interest to note that Thomson 

 (ibid., p. 139) stated that in those animals ha\ang fewer than 

 five digits (e.g. pig and ruminants) only distal epiphyses are 

 present in the metacarpals and metatarsals. 



Bardeleben regarded the prepoUex and prehallux as 

 representing a degenerate sixth digit in the manus and pes 

 respectively ; he also believed that the pisiform and the 

 tuberositas calcanei represented a seventh digit, thus advocating 

 heptadactyly for the cheiropterygium. Gegenbaur attacked 

 these views, which resulted in Bardeleben re-examining his 

 theory, but he re-affirmed it unchanged. Theories relating to 

 hexadactyly and heptadactyly have never received much 

 support, which largely exj)lains their comparative obscurity. 

 Notwithstanding this, however, it is probable that, in the 

 evolution of the cheiropterygium from the ichthyopterygium, 

 Polydactyly was characteristic of the early stages, but the 

 pentadact}^ scheme must have become stereotyped very early 

 in the history of the Tetrapoda, as at present there is not 

 sufficient evidence to make ancestral Polydactyly more than 

 an hypothesis. Baur (1896, p. 669), in commenting on the 

 subject, remarked : '' It is the general opinion that the ancestry 

 of the vertebrates with a cheirojjterygium had numerous 

 digits, and there was considerable talk of an original hexa- or 

 heptadactylism. No support to this view is given by the 

 Stegocephalia : here we never have more than five digits, 

 very often only four, and entirely hmbless forms are found 

 even in the Carboniferous." 



Again, Beddard (1902) is not a supporter of Polydactyly, 

 as he regarded the prepollex and prehallux as accessory 

 ossifications. Bardeleben (1889) described a nail associated with 

 the prepollex of the Cape jumping hare {Pedetes capensis), and 

 used the fact of the presence of such a structure with the 

 prepollex and prehallux as an important argument in favour 



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