144 EVOLUTION AND DISEASE. 
description of a remarkable anomaly in the leg of a 
girl, Among other defects she had a broad triangular 
fold of skin stretching from the thigh to the heel, as 
shown in fig. 79. The malformation was congenital 
and is in all probability unique; at any rate, it is very 
rare, for such exhaustive writers on the subject of — 
malformations in general as Forster, St. Hilaire, Alhfeld, 
and Albers furnish no parallel case. 
On superficial examination a zealous evolutionist 
might be induced to argue that we have here an 
attempt to produce a wing, or regard it as a reversion 
to the parachute-like folds of skin seen in phalangers, 
flying squirrels, or even the wings of birds. Wolff, 
however, judiciously disposes of fanciful speculation in 
this direction by correctly pointing out that, in the 
so-called flying mammals, the cutaneous folds, or para- 
chute, extends from the fore to the hind limbs, and this 
was the condition in those extraordinary extinct forms 
the pterodactyls ; indeed, no mammals, are known with 
skin-folds passing from the two segments of the hind 
limb. In birds we find a cutaneous fold passing from 
the humerus to the carpus and known as the patagium, 
which in its general appearance resembles the fold in 
the girl’s leg. Beyond this superficial resemblance these 
patagii have nothing in common, for the wing-fold in 
the bird is traversed by tendons some of which are 
remarkable for their elasticity. Thus we cannot find 
among mammals, birds, or lizards, living or extinct, any- 
thing corresponding to this curious wing-like expansion. 
We must therefore regard this skin-fold as a spontaneous 
variation, or “sport.” Even if an animal were known 
t 
