REVIEW OF LITERATURE. 13 



heredity of the maKormation is very unsatisfactory or entirely lacking 

 these cases will not be the object of further examination. 



Brachyphalangy of the second row of phalanges combined with a 

 shortening of the metacarpal bone of the thumb is instanced in Col- 

 son's case (1883), referred to by Leboucq (1896). The malformation 

 was here inherited through four generations. The examination is not 

 elaborate enough to permit conclusions to be drawn with regard to the 

 possible occurrence of different somatic types. 



A consideration of the cases of brachyphalangy reported in the 

 literature brings out the following facts : 



Several distinctly different types of brachyphalangy are known. In 

 all cases where sufficiently elaborate information is secured concerning 

 their inheritance, they are seen to be inherited as dominant Mendelian 

 characters. Some of the cases which clearly show a Mendelian inheri- 

 tance were published previous to the rediscovery of Mendel's work. 



The malformations are known only in heterozygous individuals. 

 Intermarriage between affected individuals is not so far recorded. 



In the inheritance of many cases of brachyphalangy, it is a charac- 

 teristic feature that the inherited malformation shows a very marked 

 variation in its somatic appearance. Within a family where a gene 

 for brachyphalangy is inherited, the character very often presents 

 itself under quite different somatic types. This tendency suggests the 

 assumption that the normal individuals married into the family are 

 heterozygous for different modifying genes which may change the 

 effect of the gene for brachyphalagy la question. (See pp. 58-61.) 



In hereditary cases of brachyphalangy, as well as in brachyphalangy 

 due to embryological disturbances, the second row of phalanges seems 

 to be most often and most severely affected. In the embryo it is 

 this row in which the ossification is last to begin (Fiirst, 1900; Mall, 

 1906) ; and in young individuals the cartilage epiphysis of this row 

 of phalanges is the last to complete ossification (Holmgren, 1910). 



Note. — ^The paper by H. M. Smith (1904) was overlooked until after the 

 above discussion had gone to press. 



