28 



Minor-Brachydactyly 



The variations of the bones from the normal type are shown, in out- 

 line, in Fig. 7 where A represents those of a normal finger; B, those 

 of a minor-brachydactylous finger, and C, a brachydactylous finger from 

 No. 1 family. The phalanges are numbered 1, 2 and 3 in each case 

 (3 is the terminal one which supports the finger nail). 



In C it will be observed that the second phalanx (2) and the third 

 (3) have become united into one bone : whilst in B the second phalanx 

 is short, but remains as a separate bone. 



ABC 



Fig. 7. Normal and Brachydactylous Phalanges. (Natural size.) 

 A. Normal. B. Minor-Brachydaetylous. C. Brachydactylous. 



What is the cause of this shortening ? 



Each phalanx during childhood shows, normally, a thin bony plate 

 at its base. This plate is called the epiphysis ; it is attached to the 

 larger portion — the shaft of the bone — by an intervening layer of gristle, 

 which, being transparent to the X rays, shows in a radiograph as a 

 blank space. (Figs. 8, 9.) 



