Part 49

Relations.—Superiorly, with the eyeball; inferiorly, with the inferior orbital wall.

Action.—Pulls the lower lid down.

=Quadratus Nictitans= (Fig. 26, No. B, 7). Location.—Above the eyeball along the inferior border of the upper wall of the orbit.

Origin.—From the sclerotic from the upper part of the ball.

Insertion.—To the upper part of the sheath of the optic nerve near the optic foramen.

Shape.—Broad, thin, quadrate.

Relations.—Inferiorly, with the eyeball; superiorly, with the orbital wall, with the superior oblique, and with the superior rectus.

Action.—Aids in pulling the nictitating membrane obliquely outward and downward over the forepart of the eyeball.

=Pyramidalis Nictitans= (Fig. 26, No. B, 8). Location.—Inferoposteriorly to the eyeball.

Origin.—From the lower nasal side of the eyeball.

Insertion.—The fibers converge toward the upper part of the optic nerve, into a tendon which passes through a pulley at the free margin of the quadratus. Inserts to the lower part of the margin of the third eyelid, the nictitans.

Shape.—Pyramidal; of thin layers of fibers.

Relations.—Internally, with the bony orbital wall; externally, with the eyeball.

Action.—Aids the quadratus nictitans.

=Obliquus Superior= (Fig. 26, No. B, 5). (Synonym.—Obliquus dorsalis.)

Location.—Superior to the eyeball.

FIG. 26.—Structures of the eye and nasal passage.

A. 1, The anterior turbinated bone. 2, The posterior turbinated bones. 3, Orbital gland. 4, Ophthalmic division of the fifth pair of cranial nerves. 5, Section through the cerebrum. 6, Section through the skull showing the air spaces. 7, Section through the comb. 8, Anterior portion of the upper beak. 9, Edge of the hard palate.

B. The intrinsic muscles of the eyeball. 1, Superior rectus. 2, Internal rectus. 3, Inferior rectus. 4, External rectus. 5, Superior oblique. 6, Inferior oblique. 7, Quadratus. 8, Pyramidalis. 9, Optic nerve. 10, Edge of membrana nictitans.

C. Posterior part of the eye showing at the inferior portion of the ball the pyramidalis muscle at 1, and at 2, the quadratus. 3, Optic nerve.

D. Inner view of the posterior part of the vitreous chamber. 1, Sclerotic coat. 2, Choroid coat. 3, Retina. 4, Pecten.

E. Longitudinal section through the eye of a hen. 1, Cornea. 2, Anterior chamber. 3, Scleral ring. 4, Crystalline lense. 5, Iris. 6, Retina. 7, Sclerotic. 8, Choroid. 9, Pecten. 10, Optic nerve. 11, Vitreous chamber.

F. An edge view of the crystalline lense of a hen showing it to be asymmetrical biconvex. 1, The anterior side. 2, The posterior side.

G. The upper section through the anterior portion of the anterior turbinated bone showing one complete circle and the lower a section through the middle turbinated showing one and one-half turns. ]

Origin.—From the orbital septum just back of the inner canthus, the fibers passing backward and forward.

Insertion.—Into the sclera, anterior to the sclerotic plates.

Shape.—Small, thin, fan-shaped.

Relations.—With the eyeball, superiorly; at its extremities with the superior rectus, interiorly.