ON AX ABNORMAL FROG. 87 



4. A Frog with symmetrically Abnormal Hind Feet. By 

 R. W. Harold Row, B.Sc, F.L.S., F.Z.S., Assistant 

 Lecturer and Demonstrator in Zoology, University of 

 London, King's College. 



[Received and Read November 23, 1915.] 

 (Text-fignre 1.) 



Among tlie specimens used for the teaching of elementary 

 zoology at this College, there was recently foxmd an example of 

 the Common Frog [Rana temporaria) in which both the hind 

 feet showed a curious and interesting variation. A photograph 

 of the external appearance of the two hind feet is given 

 (text-fig. 1, A), which clearly shows that on neither foot do five 

 functional digits exist ; though in both cases a small calcar, or 

 pre-hallux, as it is often called, is present in its normal position 

 in addition to four well-developed and normal toes. 



The fact that certain of the toes always present definite 

 characteristics which enable them to be indubitably identified, 

 quite apart from their actual numerical position in the series, 

 renders it quite easy to determine the identity of the digits still 

 present in the four-toed specimen. Of these characteristics the 

 most obvious distinguishes the fourth toe, which is not only 

 longer than any of. the others, but also always possesses four 

 phalanges, which is one more than the number present in any 

 other digit. In the specimen u.nder discussion four phalanges 

 can be distinguished on one toe on each hind foot, so that this toe 

 is thus marked out as the fourth of the original series, and from 

 this it can be immediately determined that the missing digit is in 

 each case the first. This identification of the digits is shown on 

 the photogi'aph. 



In view of the possibility, howes^er unlikely, that .symmetrical 

 mutilation of both hind feet might have occurred, one foot, the 

 left, has been completely dissected, and the dij^section has shown 

 that the abnormality cannot be due to injury, for the first digit is 

 unrepresented by any tissue whatever. 



During the dissection great care was exercised to determine 

 whether the muscles of the hallux were represented, and no trace 

 whatever of them was found, either in the form of small muscle- 

 masses or of fragments of muscular tissue or tendons, such as 

 would inevitably be left had the toe been bitten oft" or otherwise 

 ampvitated. The musculature of digit II (and of all the other 

 digits) was perfectly normal, and showed no signs of the inclusion 

 of muscles really belonging to digit I. Specially important is 

 the fact that fi'om the aponeurosis plantaris only four tendiiies 

 superjiciales arise, the one normally associated witli the first digit 

 being totally absent. There is also no trace of any of the bones 



