1 44 E VOL UTION 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 



