i 



14. 



CHAP. XIII.] 



DOUBLE-THUMBS : MAN. 



351 



opposed to each other (Fackenheim, Jen. Zts., xxn. p. 358, fig. iv. ; 

 Annandale, Diseases of Fingers and Toes, PI. m. fig. 25). This con- 

 dition is important as an indication that between these double-thumbs 

 there may be a relation of images (Fig. 101). 



The duplicity may be and often is very different in degree in the 

 two hands, though it is very commonly present in both. 



The description given of duplicity in the pollex applies equally to 

 the hallux, though of duplicity in the latter perhaps fewer cases are re- 

 corded. Here too the duplicity may be in all degrees of completeness. 

 An example from Axxaxdale (/. c, PL in. fig. 32) is shewn in Fig. 102. 



Fig. 102. Feet of infant, No. 514, having thumb-like supernumerary digits 

 arising from the metatarsi of the great toes. 



(After Annandale.) 



Here a thumb-like extra hallux is borne on the inner side of the meta- 

 tarsal I. Several such cases are known (cp. No. 517). 



Among the cases called by authors "double-thumb" are a certain 

 number in which the two thumbs are not equally developed, that on 

 the radial side being more rudimentary. In such a case we are entitled 

 to consider the radial thumb as an extra digit formed in Succession to 

 the normal thumb, and not as a double of it. In speaking of other 

 Meristic Series (especially mammae and teeth) we have seen that it is 

 not possible accurately to distinguish between cases of duplicity and 

 cases of change in number of the series by formation of another 

 member in the Succession. This is extremely well seen in digits. For 

 firstly several conditions intermediate between the two are recorded by 

 many authors (e.g. a case in which the radial thumb had two phalanges 

 "ankylosed" together [or rather not completely segmented from each 

 other]. Gruber, I.e., p. 480; cases in which the radial thumb had 

 only one phalanx, ibid., p. 482; Struthers, Edin. New Phil. Jour., 

 1863 (2), p. 87 ; Botjlian, Rec. de Mem. de Med. milit., 1865, Ser. 3, 

 Sin. p. Q7,Jigs.) ; and besides this there are several examples in which 

 one hand bore a clear pair of double-thumbs, while in the other hand 

 there is an extra radial digit in succession to the normal thumb (e.g. 



