46 TOPOGRAPHIC AND APPLIED ANATOMY. 



superior, external, inferior, and internal recti muscles are inserted into the corresponding portions 

 of the bulbus oculi (globe of the eye) in front of the equator by means of flat, white, glistening 

 tendons, in such a way that the average distance between the insertion into the sclera and the 

 corneal margin is 7.7 millimeters for the superior, 6.9 millimeters for the external, 6.5 millimeters 

 for the inferior, and 5.5 millimeters for the internal rectus. The long tendon of the superior 

 oblique muscle is fixed by its pulley to the fovea trochlearis and passes beneath the superior rectus 

 to be inserted behind the equator upon the upper surface of the eyeball between the attachments 

 of the superior and external recti. The inferior oblique muscle arises from the floor of the orbit 

 behind the central portion of the infraorbital margin. It runs outward and backward beneath 

 the inferior rectus and is attached posterior to the equator, at a point midway between the 

 insertion of the external rectus muscle and the point of entrance of the optic nerve. The levator 

 palpebrcB superioris almost completely covers the superior rectus and its fibers radiate to the tarsal 

 cartilage of the upper lid. [It arises from the under surface of the lesser wing of the sphenoid. 

 ED.] The tendons perforate the capsule of Tenon after the fascia of the muscles has become 

 adherent to this structure. It consequently follows that the tendinous insertions of the muscles 

 into the eyeball may be divided from the conjunctival sac (in strabismus operations), without 

 fearing that a complete retraction of the muscles will take place. [After enucleation of the eye 

 the muscles through this attachment to the capsule of Tenon may provide motion to the stump 

 and thus to an artificial eye. ED.] 



The ophthalmic artery, the only branch of the internal carotid not supplying the brain, is 

 given off from the last curve of the carotid, the convexity of the curve being anterior (see page 34). 

 It passes into the orbit through the optic foramen, in company with the optic nerve, and is situated 

 outside and below this structure. The artery then runs inward between the optic nerve and the 

 superior rectus and along the superior oblique muscle. It escapes from the orbit beneath the 

 trochlea and divides into its terminal branches, the dorsalis nasi (anastomosing with the angular 

 artery, the terminal branch of the facial) and the frontal artery. The other branches of the 

 ophthalmic are: the lachrymal, to the lachrymal gland and externally to the lids; the supra- 

 orbital, the largest branch, situated just beneath the periorbita and passing out of the orbit 

 through the supraorbital notch or foramen; the anterior and posterior ethmoidal, running through 

 the foramina of the same name; the important arteries of the interior of the eye, the long and short 

 ciliary; and the small important terminal branch, the arteria centralis retina. The vessel also 

 gives off muscular branches. 



The veins of the orbital cavity, occasionally leading to exophthalmos as a result of venous 

 stasis, unite to form two pronounced trunks. The superior ophthalmic vein, the larger of the two, 

 is situated at first at the inner side of the orbit; it passes outward between the optic nerve and the 

 superior rectus and empties into the cavernous sinus through the sphenoidal fissure. At the 

 inner canthus this vessel anastomoses with the angular vein (from the facial) and with the frontal 

 vein (see Plate 2). The inferior ophthalmic vein arises in the central portion of the floor of the 

 orbit and empties partly through the sphenoidal fissure into the cavernous sinus and partly 

 through the spheno-maxillary fissure into the region drained by the facial vein. This inferior 

 ophthalmic vein may be absent. Valves are not present in any of these veins. 



The nerves of the orbit, in addition to the optic, are the sensory first division of the trifacial, 



