20, 1 Yap and Pineda: Two Cases of Ectrosyndactyly 7 
being produced by such factors, but we can hardly say as much 
of polydactylism. 
It cannot be denied that some cases of digital deformity may be 
explained by the above considerations; but, on the other hand, 
it would be difficult to account in the same manner for malforma- 
tion of the extremities observed in amphibia, known to be devoid 
of amnion, or for those deformities which often occur sym- 
metrically in the two or the four extremities, unless we could 
conceive of a pressure resulting from some physiological con- 
dition. 
Furthermore, the occurrence of such defects in families would, 
even though discontinuous, argue for some hereditary influence 
working independently of mechanical agencies. 
Again, the deformity might also result from anomalous condi- 
tions within the ovum itself or in its environmental surround- 
ings, such as deficiency in the germ cell or injury to it resulting 
from pathological conditions in the uterus at the time when its 
organs are undergoing development and differentiation. But 
here again, while we might concede the production of monstrous 
forms from such causes, we can hardly believe that such general 
conditions would result in injury localized only in the extremities. 
It might be possible to explain these local malformations by 
defects in local nutrition; as, for instance, syndactyly due to 
deficiency, and polydactyly resulting from excessive nutrition 
of the parts. But how are we to explain the incidence in 
families? 
Atavism.—Both polydactyly and ectrosyndactyly have been 
explained by some writers under the theory of atavism. The 
intimate association of these two deformities and their extreme 
difference do not commend dual explanation. 
When the theory is applied to syndactyly some writers have in 
mind the Quadrumana. However, we found no writer who gives 
a definite statement on the subject or adduces any proof for it. 
Fotherby considered “the apposition of the great toe to the 
remaining representatives of digits and the dexterity with which 
they could be used as a near approach to the Quadrumana.” It 
is the experience of all observers that the deformed never ex- 
periences any inconvenience in the performance of his daily 
tasks; but it does not follow that such dexterity is atavistic. 
The argument put forth by some writers against atavism, that 
they have never seen normal parents give birth to deformed 
offspring, is answered by Hasselwander’s family of brachy- and 
hypodactyly, and by Wilson’s families of polydactyly, where such 
