The histological structure of the thyroid gland is relatively simple, but the
interpretation of the histological picture of individual glands examined is not
always easy. The structural relation is so variable that it is often difficult to
determine whether the gland is within normal range or not, so that interpreta.tion
tends to beeome more or less subjective and empirie. As stated by WEGELIN
(1926), the variation may depend upon the characteristic state of the thyroid
gland as a ductless gland, closely resembling an alveolar gland with a collecting
duct system and accumulating colloid in the follicles. The colloid contained may
be abundant or searee, depending upon the requirement of the animal body and
the intensity of secretory stimulation, resulting in the pattern of the parenehyma,
especially the follicles, to be also variable. This state is particularly exaggerated
in the human thyroid gland (HINTON, 1931; BIANCHEDI, 1934; ROSENKRANZ,
1935), and influenced by different eomplieated eonditions of individual life, it
be comes very difficult to analyze the histological pietures presented. Notwithstanding
eurrent interest in the physiology of the human thyroid gland in relation
to pathology and disease, little work has been done to elucidate its histology,
especially its developmental histology. 0nly some authors (HESSELBERG, 1910;
ISENscHMID, 1910; SANDERSON-DAMBERG, 1911; BÜCHNER, 1924; COOPER, 1925;
MAY, 1928; SCHAER, 1928; DE OCA, 1930; ORATOR and SCHLEUSSING, 1931; RICE,
1931; HELLWIG, 1933; SAKA, 1935) have repeated histological studies on the
human thyroid gland at different periods of postnatallife, but the human speeifie
train of histological events noted from the newborn stage to senility has not been
described in detail. No preeise quantitative data, or if any, only a little are
presented here and there. The present work constitutes the second part of studies
on the histological development of the human thyroid gland (prenatal development
- TAKI, 1958; SUGIYAMA et al., 1959a and b), based upon quantitative
measurements of the gland with non-pathological materials. It helps to elueidate
the serial steps in postnatal differentiation of the human thyroid gland, as weIl
as assists assessing the histologieal variations during different periods of life.