REVIEW OF LITERATURE. 9 



proving that they are inherited, together with cases where no such 

 information is given, but where the type described renders it almost 

 certain that they belong to the same class. 



With regard to the first class, cases where heredity is demonstrated, 

 it is of interest to notice that some of the clearest investigations 

 demonstrating the Mendelian inheritance of this malformation are 

 " pre-Mendelian " in point of time. 



As far back as in 1857, MacKinder published an account of a family 

 in which a case of brachyphalangy combined with hypophalangy was 

 inherited for six generations in a way quite typical for a regular domi- 

 nant Mendelian character. MacKinder examined individuals repre- 

 senting three of these generations. 



The most characteristic feature in MacKinder's case is a brachy- 

 phalangous condition or more often a total absence of the second row 

 of phalanges of the second to fourth fingers on both hands, combined 

 with brachyphalangy or absence of the third row on all or on the two 

 ulnar fingers with a corresponding lack or abortive condition of the 

 nails. In most of the individuals the feet are affected similarly to a 

 greater or less degree. 



The most important point, besides the Mendelian inheritance of 

 the malformation, is the fact that it manifests itself under several 

 distinctly different somatic types. 



A somewhat similar case is reported by Clarke (1915). The thumbs 

 are normal ; the second and third fingers have only two phalanges, the 

 second row being absent; the fourth and fifth fingers have only one 

 phalanx, namely, the basal one. Judging from the two radiographs 

 given, it seems probable that there really is present a very much 

 shortened rudimentary second phalanx in the fourth and fifth fingers, 

 ankylosed to the basal ones. Nails are absent. No information is 

 given concerning the feet. The malformation is found in 10 individuals, 

 covering four generations. From the short description it can not be 

 seen whether or not different somatic types are found in the affected 

 individuals. 



A third case of hypophalangy combined with brachyphalangy is 

 published by Cragg and Drinkwater (1916). The abnormality consists 

 in a symmetrical and entire absence of the distal phalanges and the 

 most extreme brachyphalangy of the second row of phalanges in each 

 digit except thumb and big toe. Nails absent. The abnormality is 

 found in 27 individuals, inherited as a typical Mendelian dominant for 

 five generations. However, 6 of the affected members of the family 

 represent another somatic type. 



In these individuals there is in addition a very characteristic bifur- 

 cation of the thumb. They belong to three different families, two in 

 each, and the thumb of their hypophalangous parent was in all cases 

 normal. The authors state that " there is little doubt that there is 



