ATAVISM OR REVERSION. 145 
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 foetal 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 bya 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 (P2thecus satanus) is drawn in fig. 80. In this 
instance the corresponding fingers on each hand were 
II 
Fic. 80.—Webbed finger in a Monkey 
(Pithecus satanus). 
