الفهرس 
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Abstract
The present work was conducted on 76 (seventy—six)
laying and non—laying hens of variable ages. They were
grouped into nine groups (group I, 20 chickens for anat
omical study, and from group II to groups IX seven birds
of each for histological and histochemical studies. Lay
ing and non—laying chickens were represented in groups
VII & IX (6 months and one year).
Morphologically, the thyroid gland appeared reddish
brown in colour and took a rounded shape in young ages
while it became oval or elliptical in adult ones. The
thyroid gland was located intrathoracically, occupied the
V-shaped area formed by common carotid artery bifurcation,
the internal carotid and vertebrovagus arteries.
The arterial supply was furnished by short branches
of the common carotid artery and its bifurcation.
The venous drainage was via small tributaries joined
the jugular vein.
The innervation of the thyroid gland was via fine
twigs arose from the vagus nerve in addition to fine
nerve filaments that arose from a sympathetic chain.
The micromorphological structure of the thyroid
gland revealed that the gland was surrounded by capsule
which was thicker in adult than in young birds. The
outer part of the capsule was formed of dense fibrous
connective tissue mainly of collagenic fibres, reticular
and elastic fibres which increased by age, also the outer
part of the capsule exhibited many fat cells forming
adipose tissue which was very distinct at 6 months and
one year of age.
The inner part of the capsule was formed of dense
connective tissue which was not constructed completely
up till 6 months and was clear at one year. The capsule
gave septulae which were very thin in youngs and incre
ased in thickenss comparatively in advanced ages.
The stroma was rich in reticular fibres with fewer
elastic and collagenic fibres which were more distinct
at one year. Also, the stroma showed many plasma cells,
lymphocytes, where they were few in young ages and incre
ased in their number according to the age. The vascularity
between the follicles was increased with advanced ages.
The thyroid follicles were of various sizes, they
increased in size with aging. The larger follicles were
mostly superifically located under the capsule, these
peripheral large follicles were lined with flattened
epithelium with flat nuclei. The small follicles usually
took a central position, they were lined with cuboidal
epithelium with slightly stained cytoplasm and spherical
centrally situated nuclei.
Parafollicular cells in young ages were indistinct,
at one month of age, they were easily recognized. They
appeared pyramidal or polyhedral in shape with faintly
distinct borders, their nuclei were large and spherical,
the cytoplasm appeared faintly stained. The parafollicul~
cells were either singly or parietally situated in be
tween the follicular cells or in groups between the
thyroid follicles, some of the singly scattered parafol—
licular cells show~ darkly stain~ nuclei.
In a close association with the thyroid capsule the
ultimobranchial body had been lain, where it was smaller
in young ages and increased by advance of age, with cystic
formation in the centre. Ultimobranchial body was inve
sted in fibrous capsule and showed outer highly cellular
zone and inner zone of vacuolated polyhedral cells hav
ing faintly stained nuclei.
Ultimobranchial body exhibited its highest develo
pment with high vascularity represented by many engorg~
blood sinusiod. body than non laying ones. Though the variation in the
thyroid gland and parafollicular cells showed less marked
variation except in laying hens of one year where they
had a more active larger sized, slightly stained para—
follicular cells.
The histochemical finding:
The thyroid gland showed negative reaction to PAS
at age 6 months and one year, the parafollicular cells
showed positive reaction in colloid and basement membrane.
Thyroid follicular cells and parafollicular cells
showed negative reaction to glycogen in both young and
adult ages. Also, a negative reaction to oil red 0 was
revealed, while the capsule of the gland showed positive
reaction to oil red 0.
The gland showed slight reaction to acid phosphatase
till 8 weeks of age. At 6 months and one year it showed
a slight reaction to acid phosphatase but slightly more
in parafollicular cells.
The thyroid gland gave low level of reaction for
alkaline phosphatase, Glucose-6--phosphatase, 80Ff and N.S.E.,
with advance of age the intensity of the reaction was increased except SDH where it was moderate in reaction
at 1 year of age. parafollicular cells gave a stronger
reaction to G-6-P-ase.
Regaپ}ding the histochemical reactions in laying arid
non-laying hens, they were not variable except for SDH
at one year of age, in doing so it was lesser than 6
months of age.