16 J. A. BADERTSCHER 
the right ultimobranchial body. A few large follicles are found 
near the caudal end of the thyroid gland. 
Pig 15 days old (fig. 2). The thyroid gland is 10.5 mm. long 
and its greatest width is 6.3 mm. It tapers to a blunt point at 
each end. Only the right ultimobranchial body is present. It 
is embedded deeply below the dorsal surface in the posterior 
half of the thyroid gland. It is represented by two areas which 
are composed of syncytial cords and masses in which follicles 
containing colloid are quite numerous, but on an average much 
smaller than the majority of follicles in the immediate neigh- 
borhood of these areas. The more anteriorly located and larger 
of these areas (fig. 2, U.) extends through a series of eighty-five 
sections, while the more caudally located one extends through 
sixteen consecutive sections. Thirty-six sections intervene be- 
tween the two areas.. The structure of the nuclei in these areas 
is identical to that of the nuclei in the cells composing the 
follicles. In the caudal fourth of the thyroid gland there are 
many very large follicles which are located chiefly in the dorso- 
lateral margin of the gland. 
Pig 28 days old. The thyroid gland is 11.1 mm. long and its 
greatest width is 7.7 mm. It tapers to a blunt point at each 
end and its more bulky portion is crescent in shape in cross- 
section. Both ultimobranchial bodies are present. They are 
located just below the dorsal surface in the caudal portion of the 
middle third of the thyroid gland, lateral to its medial plane. 
The right one is similar in structure to the ultimobranchial body 
in the thyroid gland of the 15-day-old pig. It extends through 
a series of sixteen sections. The left ultimobranchial body is 
composed largely of an attenuated syncytial mass in which are 
found a few small follicles. It extends through a series of 
thirty-eight sections. 
In the immediate neighborhood of the left ultimobranchial 
body are found a few very large follicles. Many very large 
follicles are present in the taudal fourth of the thyroid gland. 
These are located chiefly near the dorsal and dorsolateral border 
of the gland, excepting near its caudal end where they are 
scattered throughout the entire thickness of the gland. 
