_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. [Illustration: 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. _Action._—Rotates the eyeball. =Obliquus Inferior= (Fig. 26, No. _B_, 6). (Synonym.—Obliquus ventralis.) _Location._—Inferior to the eyeball. _Origin._—From the interorbital septum near the inner canthus of the eye. _Insertion._—By a broad expansion to the inferior portion of the eyeball. _Shape._—Tendinous at its insertions; fan-shaped as it passes downward and outward. _Relations._—Internally, with the eyeball; and externally, with the bony orbital wall, with the inferior rectus muscle, inferiorly. _Action._—Aids in rotating the eye; opposes the obliquus superior.