الفهرس 
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Abstract
The results presented in this investigation elucidate the
histogenesis of the buffalo (Bos bubalis) thyroid gland using 61
fetuses and embryos at different ages ranging from 37-300 days (2
em _ 100 em CVRL) intrauterine as well as the thyroid gland of 15
buffaloes ranging between 1.5 months - 10 years old. obtained
from the slaughter house. Serial sections of 4 - 6 Um thick were
prepared and stained with different histological stains.
The bilateral thyrDid primordium at the early ages of
development appeared as mass of endodermal cells arranged in the
form of cords and clumps supported by connective tissue elements.
By development of the embryo, the size of the thyroid lobe
increased and the cell cords grow due to the active proliferation
of the endodermal cells. during the growth of the cords.
fragmented into shorter portions or clumps. from the cell cords
and clumps. primitive follicles were formed at 42 days (3 em
CVRLl.
At 76 days old (10.5 em CVRLI. true follicles containing
colloid were seen. As the development proceeded. the size of the
lobe increased due to increase in number and size of the
foll icles as well as the supportive connective tissue. Some new
follicles were originated from the parent follicles by budding as
well as from the ultimobranchial tissue. The follicles took
characterist ic distribution wi thin the lobe, the small foll ieles were seen in the periphery while the larger ones were located
centrally. Some follicles showed signs of degenerative changes at
senile age.
At 42 days old embryos (3 cm CVRL) , fine PAS-positive
granules appeared either diffused or in the form of fine droplets
in the epithelial cell cords, at 76 days old (10.5 em CVRL) ,
intra-luminal colloid was seen. The amount of the colloid was
varied between the different follicles when the age was
increased. The colloid appeared homogeneous acidophilic after H&E
and PAS stains except for some macrophages, desquemated cells and
some vacuoles. The latter appeared in the colloid at the late
time of pregnancy and during the postnatal life.
Few light cells or parafollicular cells were seen firstly at
49 days old embryos (4.5 cm CVRL) scattered between the cell
clumps. They were easily observed at 65 days old fetus (12.5 cm
CVRL) either singly or in groups between the cell clumps as well
as in the follicular wall. They were large spherical. oval or
polyhyderal with light staining cytoplasm and large nuclei.
Mitotic cell divisions were seen in the light cells. They were
originated from the ultimobranchial body.
The ultimobranchial cysts were observed at 49 days old embryo
(4.5 cm CVRL). Discrete ultimobranchial body was seen as compact
cell mass enveloped by connective tissue beside the thyroid lobe
at 146 days old fetus (32 cm CVRL). At 171 days old fetus (43 em
CVRL) group of cells from the ultimobranchial body were seen
entering the thyroid lobe forming new follicles. Some large cells with light staining cytoplasm were observed in the cyst wall. The
lumina of some cysts contained colloid-l ike material with some
cell debris. The ultimobranchial cysts persisted in postnatal
thyroid up to seni l e age but some of them showed degenerative
changes.
The stroma of the gl and was composed of mesenchyma1 cell s
with v”,ry fine reticular fibers at 37 days old embryo (2 cm
CVRL), then differentiated into fibroblasts and numerous fine
reticular and co l Laq eu i c fibers at 109 days old fetus (16 cm
CVRL). The capsule increased in thickness with increasing of the
ag”, of the fetus and was mainly formed of collagen, reticular
fibers and connective tissue cells with some blood vessels.