14 J. A. BADERTSCHER 
In the description of the following stages special attention will 
be given: 1) to the structure of the ultimobranchial bodies and 
to their location in the thyroid gland, and 2) to the location and 
extent of areas of unusually large (cystoid) follicles. Since in 
the embryonic material it was found that cystoid follicles may 
develop in the ultimobranchial bodies, the latter consideration 
is of importance. 
Pig at birth. The thyroid gland is 9.3 mm. long and its 
greatest width is 4.8 mm. Caudally it terminates in a rather 
blunt point, while the anterior portion is drawn out into a slender 
streamer. The greater portion of the bulk of the gland is thus 
located in its posterior half. The more bulky part of the gland 
is crescent in shape in transverse sections. In the middle third 
of the left lateral half of the thyroid gland the ultimobranchial 
body is represented by three small areas which are composed of 
tortuous syncytial cords and masses quite closely packed to- 
gether. These areas are embedded beneath the dorsal surface 
of the gland lateral to its medial plane, a position usually 
occupied by the ultimobranchial bodies in the later embryonic 
- stages. Anterocaudally, they extend through eight, six, and 
twelve consecutive sections, respectively. The most anteriorly 
located of these areas is free from colloid and lies in a field of 
follicles that are on an average smaller than the average size of 
the majority of follicles present in the thyroid gland. In the 
central and caudal areas the colloid is just beginning to form. 
On account of the absence of colloid in one and its scanty amount in 
the other two of these areas, they stand out sharply from the thy- 
roid follicles immediately surrounding them. No difference could 
be observed between the structure of the nuclei in these areas and 
the nuclei in the cells composing the follicles. In the right lateral , 
half of the thyroid gland the ultimobranchial body is absent. 
1 As this work is practically a continuation of a previous investigation (18) 
by the author of the ultimobranchial bodies in pig embryos, it was deemed 
unnecessary to repeat an historical sketch of this subject in this article. Also 
the bibliography includes only those references to articles in which may be’ 
found more orless definite statements concerning the fate of the ultimobranchial 
bodies. If an extensive bibliography on this subject is desired, reference should 
be made to the, works of Verdun (’98) and Grosser (12). 
