Breitenbecher : Short Thumbs 



17 



A NORMAL HAND 



Figure <). The comparison between short and normal thumbs was made 

 by taking the average of the measurements of the bones of five normal 

 hands. The metacarpals of the short thumbed hands were found to be 

 longer, and the terminal phalanx of the short thumb much shorter than the 

 corresponding bones in the normal hands. It is this short phalanx of the 

 thumb, and the unusually long metacarpals of the fingers that are inherited. 



of these the first five were normal ; 

 the sixth measured was a radiograph 

 of Abnormal 7. From a compari- 

 son of the abnormal with the five 

 normal pairs, one discovers a differ- 

 ence in the metacarpals, and in the 

 second and third phalanges, but much 

 closer agreement in all six pairs of 

 hands as regards the first phalanx. Be- 

 cause of this approximate agreement it 

 seemed that the essential relations could 

 be brought out better l^y expressing all 



measurements as ratios in terms of the 

 first phalanx of the digit in question. 

 These ratios are given on the right of 

 Table 2, under the heading, "Calculated 

 ratios." 



To obtain a more direct comparison 

 between the abnormal and normal 

 bones of each digit, the ratios obtained 

 for the five normal cases were added 

 together and an average normal ratio 

 obtained. These averages for the 

 normal bones are compared with the 



