الفهرس 
ACKNOWLEDGEMENT
Anatomy of the Eye of Little OwlOnly 14 pages are availabe for public view
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Abstract
The present study is concerned with the functional Anatomy and morphology of the eye of the little owl Athene noctua and is performed through the studying of the following points:
I- Anatomical study of the eye
A full description of the morphology of the eye of the little owl Athene noctua is given, and from the functional point of view, the following parts are described.
1- The brain case of little owl contains large antero-lateral cavity (orbit) which is separated by thick interorbital septum. The orbit is delimited anteriorly by the ectethmoid bone, dorsally by the frontal bone, antero-dorsally by the lacrimal bone, posteriorly by the laterosphynoid and ventrally fused with the parasphenoid rostrum.
2- The eyeball: little owl Athene noctua possesses a large tubular eye which is anterolaterally located within the orbit of skull. The anterior portion of eye of little owl (Athene noctua) protrudes from the skull and supported by convex scleral ossicles which their number 13-14 segments. The scleral ossicles exhibit asymmetry; their temporal segments expanded more than their nasal one and the dorsal segments are smaller and shorter than the ventral ones .while, the posterior portion of the eyeball supported by the sclera cartilage.
3- The accessory organs of the eye which include; the eyelids (upper, lower and third eyelids) and the orbital glands.
a- The upper and lower eyelid
The little owl (Athene noctua) has movable eyelids (upper eyelid, palpebral dorsalis and lower eyelid, palpebral ventralis). The upper eyelid is shorter and thicker more than the lower one. The palpebral margin ”plica marginalis” of each eyelid is deeply pigmented and segmented into number of folds.
b- The nictitating membrane
The nictitating membrane of little owl is well developed semi-transparent and mobile organ which formed as reduplication of conjunctiva. The free margin of this membrane is a thick and dark edge which is extended obliquely to the anterior canthus which is almost visible during rest of action beneath the palpebral margin of upper.
c- The orbital glands
The eye of the little owl contains two types of orbital glands; Lacrimal and Harderian gland. The lacrimal gland is pink in color, cylindrical in shape and slightly dorso-ventrally compressed and situates on the dorsal rim of the orbit and covered completely by the periorbital sheet. Meanwhile The Harderian gland of the little owl is a flat and elongated flask-shaped gland with light pink color. This gland locates antero-ventro-medial surface of sclera cartilage, ventral to the ventral oblique muscle and dorsal to the pyramidalis muscle. Both glands are compound tubuloalveolar gland which consists of columnar cell in the lacrimal gland and cuboidal in the other gland.
4- The lens
The eye of the little owl (Athene noctua) is characterized by large, spherical and biconvex lens. The corneal surface of lens is more convex than its vitreal one. The lens of little owl consists of three parts; anterior lens epithelium, central body annular pad between this pad and central body there are vesicular space. As well as, the whole lens is enveloped by thin capsule of collagen fibers and also exhibits positive PAS reaction
5- The eye muscles
The eye muscles of the little owl (Athene noctua) can be classified into two functional groups; 1- Extraocular muscles that move the eye itself, and 2- Accessory ocular muscles that control on the movement of the eyelids and nictitating membrane.
a- Extraocular muscles
six extraocular muscles effect on the movement of the eye include; muscle Rectus Dorsalis, Oblique Dorsalis, Rectus Ventralis, Oblique Ventralis, Rectus Medialis, and Rectus Lateralis. These extraocular muscles attach on the interorbital septum around the optic nerve and insert on the global. In little owl, the rectus medialis and oblique dorsalis muscles cooperate in pulling of the eye in anterior and dorsal direction while the antagonistic movement is done by the contraction of the ventral oblique. The contraction of dorsal oblique of little owl may elevate the eye ball and also causes in-cyclo rotation toward the anterior canthus while the antagonistic movement is done by the contraction of the ventral oblique muscle
b- Accessory ocular muscles:
These muscles control on the movement of the eyelids and nictitating membrane that including muscle Levator palpebral Superioris (LPS), Levator anguli oculi (LAO), Retractor anguli oculi lateralis (RAOL), Retractor anguli oculi medialis (RAOM), Depressor palpebral inferioris (DPI), Quadratus (Qm),and Pyramidalis (Pm).
II- the histological investigation of the eye and it’s the accessory organ
A full description of the different structure of the eye as well as its accessory organ was studied by using histological techniques.
A- The eye ball is composed of three layers
The outer layer (Fibrous Tunic) which includes sclera and cornea. The middle layer (Vascular Tunic) which consists of ciliary body, iris and choroid, and The inner layer ( Nervous Tunic)
1- The outer layer (Fibrous Tunic) The cornea of the little owl (Athene noctua) is forms as anterior extension of periosteium of sclera ossicles
2- The middle layer (Vascular Tunic) is the middle layer of the eye which is composed of three regions: the choroid, the ciliary body, and the iris.
• The anterior surface of iris of little owl is covered by one layer of discontinuous flattened cells, while the posterior surface is composed of two layers of epithelial cells. The outer layer of posterior surface is composed of cuboidal epithelium fill with heavily pigmented granules, while the inner layer consists of flattened cells with oval nuclei. Between these epithelial layers a highly vascularized connective tissue and two layers of muscle bundles are distributed
• The ciliary body of the little owl (Athene noctua) forms triangular folds of loose connective tissue rich in collagen and elastic fibers vessel and melanocytes. These folds are covered by two layers of epithelial cells.
3- The inner layer ( Nervous Tunic)
The retina of the little owl (Athene noctua) is composed of outer pigmented and the inner nervous layers. as well as Three distinct photoreceptors are observed; rods, single cone and double cones.
B- structure of the eye lids
The structure of both upper and lower eyelids is very similar in the little owl and characterized by:
1-The skin surface of both eyelids of little owl is composed of keratinized squamous epithelium
2- The cell-layered of the skin surface is varied from one to two layers in lower eyelid while it reached approximately three to four layers in upper eyelid. Thus, the lower eyelid in little owl appears very thin more than upper lid.
3-The conjunctiva of eyelids in little owl changes from stratified squamous type to stratified cuboidal
The epithelium of conjunctival surface of eyelids containing numerous goblet cells which exhibits purple color with PAS reaction and slightly bluish color with toludine blue stain
C- The nictitating membrane
The nictitating membrane of little owl (Athene noctua) reveals that both surfaces of nictitating membrane are covered by folded stratified epithelium The free margin and palpebral surface of the nictitating membrane are covered by non-keratinized squamous epithelium while its bulbi surface is covered by stratified columnar epithelium with dome shape Moreover, numerous of pigmented granules are interspersed only between the epithelial cells of free margin.