6 The Philippine Journal of Science 1922 
fourth to the eighth year, and union to the shafts takes place 
at the nineteenth to the twenty-first year. 
In our two cases we found no distinct epiphyseal lines except 
in some of the phalanges in Case II. This is in accord with the 
above embryological facts. The discrepancy in our cases from 
that of normal embryological development of bones lies mainly 
in the hypoplasia of some of the metacarpals, metatarsals, and 
phalanges, and in the total absence of some of the metatarsals 
and phalanges. 
It can be deduced from the above considerations that any arrest 
of the bony development of digits in either extremity must have 
taken place before the eighth week of embryonic life. 
The question of the etiology of these and similar deformities 
has been ably considered by several authors. The discussions 
mainly resolve themselves into four theories; namely, the theory 
of maternal impression, that of external influence, that of ata- 
vism, and that of heredity. 
Maternal impression.—This theory may be considered only 
because of its historical value. It is closely linked with super- 
stition, and entirely lacks scientific basis. This is at once ap- 
parent if we keep in mind that in most of the cases reported and 
explained under this theory the impression occurred after the 
normal period of ossification of these parts. 
External influence.—Under this theory many authors include 
such influencing factors as mechanical agencies, pathological 
conditions in the ovum or its environment, etc. Of these, the 
mechanical theory is the most widely discussed. Malformations 
are explained by internal or externa] injuries to the embryo 
while in utero, resulting from such agencies as amniotic adhe- 
sions, cord defects, etc. It is probable that many cases of 
amniotic adhesions result from pressure upon or disease of the 
amnion. It is a conceivable fact that adhesions between the 
amnion and the embryo can mechanically prevent or pervert 
the growth of the parts affected; certainly there are on record 
cases of digital amputations resulting from adhesive entangle- 
ments with the amniotic bands. Moreover, pressure upon an 
extremity would indeed cause it to be stunted, and such pressure 
may result from a variety of causes, such as abdominal or 
uterine tumors, tight lacing, etc. 
Cord defects may also be considered as causing amputation of 
digits, or other similar deformities of the extremities. Some 
cases of so-called spontaneous amputation have been attributed 
to them. We can imagine a few cases of ectrosyndactyly as 
