16 



The Journal of Heredity 



X-RAY OF THE SHORT THUMBED HANDS 



Figure 8. The long bones of the palm of the hand are termed metacarpals, the three 

 finger bones are the phalanges, the first phalanx being at the base of the finger. While 

 this picture is slightly more reduced than that of the normal hand (Figure 9), it enables 

 direct comparison to be made between the bones of the two hands, as the reduction is such 

 that the metacarpals of the thumbs of the two hands are of exactly the same length. 



The result of this observation indi- 

 cates that on the average the end of 

 the normal thumb coincides with the 

 joint at the union of the first and 

 second phalanx of the index finger. 

 The abnormal members of this family 

 have thumbs the ends of which, on 

 the average, coincide with the joint at 

 the junction of the metacarpal and 

 first phalanx of the index finger. 

 Briefly, the abnormal thumb is short- 

 er than the normal by the length of 

 the first phalanx. 



To study this al)normality in great- 

 er detail and to determine the in- 

 ternal efifects of this mutation, it 

 seemed desirable to have x-ray pic- 

 tures of the hands of one of these 



aft'ected individuals. This radiograph 

 was then compared with two radio- 

 graphs of normal thumbs, as well as 

 with three skeletons. It was thought 

 possible that the shadows of the 

 bones might interfere with the tech- 

 nique of measuring, but it was found 

 that a radiograph is a source of in- 

 formation as accurate as the bones 

 themselves. 



A comparative analysis was made 

 with one abnormal (Abnormal 7) and 

 the five above-mentioned normal right 

 hands, by measuring the length of 

 the bones of each digit. Complete 

 data regarding these measurements 

 are given in Table 2. The number of 

 hands measured in all was six pairs. 



