Pip J. A. BADERTSCHER 
from the median thyroid anlage. The caudal end of the thyroid 
gland in some of the postnatal pigs (pig at birth, pig 15 days old, 
and young adult hogs no. 1 and 2) contains many large follicles. 
This feature apparently bears with it a significance when it is 
correlated with the fact that in some of the comparatively early 
embryonic stages the caudal portion of the tripartite complex is 
largely composed of ultimobranchial bodeis. 
Although the evidence of an interrelationship between the 
large follicles and the ultimobranchial bodies in postnatal pigs 
is circumstantial, yet when this evidence is correlated with their 
development in connection with the ultimobranchial bodies in 
some of the later embryonic developmental stages, it appears 
that the ultimobranchial bodies are largely responsible for the 
large (cystoid) follicles. 
In conclusion, it can be said that since the ultimobranchial 
bodies fuse with the thyroid gland and also form colloid the 
boundary between these structures and the gland becomes ob- 
literated, so that it is impossible to determine the exact relative 
proportion that is contributed to the thyroid gland by the 
ultimobranchial bodies and the median thyroid anlage. Owing 
to the variable developmental behavior of the ultimobranchial 
bodies, the relative proportion they contribute to the thyro‘d 
gland undoubtedly varies in different pigs. It is, however, 
quite evident that only a relatively small portion of the gland is 
derived from the ultimobranchial bodies. 
