ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 15 
Unusually large follicles are present in both lateral halves of the 
caudal fourth of the thyroid gland. These are located mainly 
near the dorsal and dorsolateral surface of the gland. A few 
very large follicles are located near the most caudally located 
area of the ultimobranchial body. Also an area of very large 
follicles (extending through a series of thirty-four sections) is 
present in the caudal portion of the middle third of the right 
lateral half of the thyroid gland just below its dorsal surface. 
Pig 7.5 days old (fig. 1). The thyroid gland is 15 mm. long 
and its greatest width is 6.8 mm. The greater portion of the 
anterior half of the thyroid gland is in form a slender band, so 
that by far the greater portion of its bulk les in the posterior 
half of the gland. The more bulky portion of the gland is 
crescent in shape in transverse section. Traces of both ultimo- 
branchial bodies are present in the caudal fourth of the thyroid 
gland. The left one is represented by three oblong areas com- 
posed of closely packed syncytial cords and masses which are 
almost free from colloid. The nuclei in the syncytium have a 
structure identical to the structure of the nuclei in the cells 
composing the follicles. Anterocaudally, these areas extend 
through nineteen, seven, and thirty consecutive sections, re- 
spectively. The most anteriorly (fig. 1, U.) and caudally lo- 
cated of these areas are partially exposed to the free surface 
on the dorsal border of the thyroid gland, while the centrally 
located one is embedded only a short distance below the dorsal 
surface of the gland. The ultimobranchial body on the right 
side has a structure similar to the left one. It extends through 
a series of ten sections and is entirely embedded below the 
dorsal surface of the thyroid gland. 
In the left lateral half of the thyroid gland and just anterior 
to the ultimobranchial body represented in figure 1 is the caudal 
termination of an elongated area containing many large (cys- 
toid) follicles. This area of large follicles is located just below 
the dorsal border of the thyroid ‘gland and extends through 
seventy consecutive sections. Very large follicles are also found 
in the immediate neighborhood of the centrally located area of 
the ultimobranchial body. Two rather large follicles lie near 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, NO. 1 
