106 Cc. H. DANFORTH 
due not to any inherent peculiarity of the structures themselves, 
but rather to the conditions under which they develop. The 
shortening of the soft parts, seemingly secondary is more 
probably the primary factor in causing brachydactyly. In the 
adult foot, however, the bony framework provides an accurate 
index of toe length. 
As already indicated, the reduction in the skeletal elements 
is both qualitative and quantitative. It may be that this 
reduction does not take place in the same way in all short-toed 
specimens, but a series of grades may be described which 
seem to represent successive steps in the process. 7 
The first degree of shortening represented by the least pro- 
nounced type is characteristic of the majority of brachydactyl 
specimens. Here all of the phalanges are present, but the 
fourth, or sometimes the third, is more or less shortened. The 
amount of shortening in these phalanges varies greatly and can 
often be estimated in the living chick. It has not been possible 
to determine accurately whether or not the other phalanges are 
also shortened, although it is probable that they are, especially — 
- the fifth since the nail is almost always abnormally small. The 
fact that the fourth, or occasionally the third, phalanx is the 
one first affected suggest that the reducing factor is most effective 
at the time these phalanges are being laid down, viz: on the 
ninth, or occasionally the eighth day. 
The second degree, found in slightly over a fifth of the cases 
studied, shows the first numerical reduction in the phalanges. 
Here the third and fourth segments are replaced by a single 
element. The resulting cartilage is commonly a slender rod 
slightly longer than a normal fourth which it otherwise re- 
sembles. This cartilage also varies in length so that there is 
some fluctuation within this grade. It has not been possible to’ 
determine with certainty whether the coalescence of the two 
elements is due to one cartilage forming from the substance 
that normally gives rise to two, or whether both elements form 
separately and then fuse. The specimen shown in figure 4 seems to 
favor the latter alternative, but where the adult organ presents 
an unlimited series of gradations it is impossible to say in the 
