REGION OF THE EYE. 



81 



Muscles of the Orbit. Six muscles are connected with the eyeball, 

 four straight and two oblique. One muscle, the levator palpebrcz, goes to the 

 lid. The four recti muscles, superior, inferior, external, and internal, arise from a 

 common tendinous origin, forming a ring or tube called the ligament of Zinn. 

 This ligament or tube surrounds the optic foramen and is attached to the opposite 

 side of the sphenoidal fissure. Through it run the optic nerve and ophthalmic artery, 

 the third, fourth, and the nasal branch of the ophthalmic (fifth) nerve. 



The levator palpebrcs and superior oblique arise to the inner side and above the 

 optic foramen close to the origin of the other muscles. The superior oblique, after 

 passing through its trochlea or pulley at the inner upper angle of the orbit, continues 

 downward, backward, and outward between the superior rectus and the eye, to be 

 inserted above the extremity of the inferior oblique. 



Ethmoidal cells 



Sphenoidal sinus 



Superior oblique 

 muscle 



Superior rectus 

 muscle 



Levator palpebrse 

 superior muscle 



Superior ophthal- 

 mic vein 



Lachrymal gland 



"% 

 FIG. 96. The roof of the orbit has been removed, showing the contents. 



The inferior oblique arises from the anterior edge of the orbit just to the outer 

 side of the lachrymal groove. It passes outward, upward, and backward, over 

 the external surface of the inferior rectus, to be inserted beneath the external rectus. 



The recti miiscles insert into the sclera 5 to 7 mm. back from the cornea. In 

 the operation for internal squint or strabismus, the internal rectus muscle is cut. 

 It possesses the longest tendon of insertion, while the external possesses the shortest 

 The recti muscles pull the eyes toward their respective sides. The superior oblique 

 turns the cornea down and out and rotates it inwardly. The inferior oblique turns 

 the cornea up and slightly out and rotates the eye outward. A disarrangement of any 

 of these muscles produces diplopia or double vision. 



Blood-Vessels of the Orbit. The arteries of the orbit are derived from the 

 ophthalmic artery, which breaks up into its various branches soon after it passes through 

 the optic foramen. In enucleation of the eye there is practically no bleeding, 

 because the arteria centralis is the only one divided, and it is small. In evisceration, 

 or cleaning out of the contents of the orbit, the main trunk of the ophthalmic will 

 not be cut unless the very apex is invaded. Hemorrhage is readily controlled by 

 packing gauze into the orbital cavity. 



The veins of the orbit are the superior and inferior ophthalmic. The former is 

 much the larger and more important. It not only drains the upper portion of the 

 orbit, but communicates directly with the angular branch of the facial, at the inner 

 canthus of the eye. The infection of erysipelas sometimes travels along these veins 

 directly from the nose, face, and scalp without, to the cavernous sinus and meninges 

 6 



