الفهرس 
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Abstract
INTRODUCTION
AND AIM OF THE WORK
The orbital glands in different mammals exhibit considerable
differences and similarities as regards the structure and function.
The orbital glands consisted mainly of :
- The Harderian gland.
The lacrimal gland.
The Harderlan gland is one of the major orbital glands of
vertebrates (Walls, 1942). This gland has been considered as a
sonrce of lubricant for the eye (Cohn, 1955 and Kennedy, 1970)
and the bulk of its secretory product is of a lipid nature in mammals
(Carriere, 1985). Fnrthermore, the gland is a known sonrce for
porphyrin pigment biosynthesis as it manufactures and stores
porphyrin (Lin and Nadakavakaren, 1982).
The lacrimal gland is found in animals who live in air, but
in fishes for example, there is no lacrimal gland, as the water in
which they live act in place of tears (Last, 1968). It is presumed
that the lacrimal gland is the sonrce of watery layer ofhuman tears
(Gillette, Allansmith, Greiner and Janusz, 1980). They also stated
that the main lacrimal gland is the sonrce of stimulated tears, while
the accessory lacrimal glands provide the basic watery layer of
llllStimulated tears. Whereas, under normal circumstances, the tear
fluid forms a thin layer approximately 7 -I 0 ).liil thick that covers the
corneal and conjunctival epithelium to wet their surfaces (Tabbara
and Okumoto, 1982).The nictitating gland is another orbital gland which is found
to be embedded in the substance of the third eye lid in some
manrmals as in dogs (Miller, Christensen and Evans, 1964).
The present study aims to throw some light on the siructural
differences and similarities in the orbital glands of some manrmals
(Rat, Rabbit and Human) by histological and histochemical
techniques.