BRACHYDACTYLY IN THE FOWL 105 
Tracing the condition back in the development of the chick, 
we find, as already stated, that brachydactyl can be recognized, 
at least in many cases, as early as. the ninth day, when the 
fourth toe in certain individuals can be seen to be conspicuously 
shortened. It has not been possible to determine whether or 
not the shortening is actually present at an earlier date. The 
cartilage of the third phalanx of the fourth toe is laid down 
during the 8th day. The fourth and sometimes the fifth car- 
tilage are formed on the 9th day. By the end of the 10th day 
all of the phalanges to develop are present in cartilages. Definite 
reduction in the number of cartilages cannot be recognized with 
certainty earlier than the tenth day. 
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Fig. 3 Foot-prints of (A) brachydactyl and (B) normal left feet. In A the 
absence of one phalanx in the fourth toe is revealed. 
The fact that brachydactyly is apparent at the time when 
cartilages are formed, if not actually before then, would seem to 
indicate that the reduction of the skeleton takes place in re- 
sponse to conditions already manifest in the toe, and not as a 
result of any factor acting specifically on cartilage or bone forma- 
tion. In other words the cartilage anlagen form while subjected to 
a kind of compression resulting from the shortening of the toe. 
The consequent reduction in the cartilages, and the correlated 
changes in ligaments, tendons, etc., would therefore seem to be 
