ZYGODACTYLY AND ITS 

 INHERITANCE 



Adolph H. Schultz 



Carnegie Institution of Washington, Dept. of Embryology 

 Johns Hopkins University, Baltimore, Md. 



NORMAL WEBBED TOES 



In certain early developmental stages the 

 human foot is normally webbed. Very soon 

 afterwards the webs disappear and the toes be- 

 come separated. If this reduction of the webs 

 fails to take place the condition of web-footed- 

 ness results. Note that this normal pre-natal 

 webbing is greater between the second and 

 third toes than between the others. (Fig. 7.) 



THE last two volumes of the 

 Journal of Heredity each con- 

 tains a report on the inheritance of 

 web-formations between the second 

 and third toes in man^'- and the writer 

 has come across several other articles, 

 scattered through the literature, in 

 which this anomaly has been traced 

 through a number of generations. It 

 seemed desirable to collect these vari- 

 ous studies, each of which was made 

 independent of other recorded cases, in 

 order to be able to draw wider conclu- 

 sions from the larger material, to cor- 

 rect some slight misstatements made 



1 Hurlin, R. G. 1920. A case of inherited syndactyly in man. J. of Heredity, vol. XI, pp. 

 334-335. 



2_Schofield, R. 1921. Inheritance of webbed toes. J. of Heredity, vol. XII, pp. 400-401. 



113 



A SIMANG'S FOOT 



Webbing occurs repeatedly between the 

 second and third toes of these apes found in 

 Borneo and Sumatra, and it is also found in 

 other animals. It represents an arrest in normal 

 development, in contrast to conditions like 

 split-foot, characterized by union of the boney 

 elements of the hand or foot, which are brought 

 about by deep developmental disturbances. 

 (Fig. 8.) 



by previous authors, and to stimulate 

 further collecting of such cases. 



Before taking up the question of 

 heredity, it might be well to consider 

 in more detail the anomalous condition 

 itself. In figure 7 is shown a very early 

 developmental state of the human foot. 

 From this it can be seen that during 

 growth the toes pass through a phase 

 in which they are normally joined by 

 webs. Between the second and third 

 toes this web-formation extends slightly 

 farther than between any of the others. 

 Very soon afterwards the toes become 

 separated, i.e., the webs are reduced to 



