ATAVISM OR REVERSION. 



to possess such a web, there would be another strong 

 argument against its reversionary character, viz., that 

 in the embryo the two segments of the limb are not 

 united or in any way connected by a cutaneous fold ; thus 

 we have not to deal with a persistent fcetal structure. 



Whilst dealing with skin-folds it may be of interest 

 to draw attention to a 

 not infrequent example of 

 webbing. In the human 

 subject it is not uncommon 

 to meet with individuals 

 possessing two or more 

 fingers united to an abnor- 

 mal degree by a web. Nor- 

 mally our fingers are webbed 

 as low as the middle of the 

 first phalanx. The gorilla 

 has a web extending to the 

 first joint of the index and 

 middle finger, and the Sia- 

 mang gibbon has its second 

 and third toes webbed as far 

 as the distal end of the first 

 phalanx ; the seal and orni- 

 thorhynchus have a broad 

 web to the digits of manus 

 and pes. Abnormally webbed fingers and toes are not 

 peculiar to man ; they occur in monkeys, and a good 

 specimen of this malformation which occurred in a 

 monkey (Pithecus satanus) is drawn in fig. 80. In this 

 instance the corresponding fingers on each hand were 



ii 



