THE ORBITAL REGION. 397 



artery, the periosteum of the orbit, and, in the lid, with the inner surface of 

 the tarsal ligament ; by its under surface, with the Superior rectus, and, in the 

 lid, with the conjunctiva. A small branch of the third nerve enters its under 

 surface. 



The Superior rectus, the thinnest and narrowest of the four Recti. arises from 

 the upper margin of the optic foramen beneath the Levator palpebrge and Superior 

 oblique, and from the fibrous sheath of the optic nerve, and is inserted by a 

 tendinous expansion into the sclerotic coat, about three or four lines from the 

 margin of the cornea. 



Relations. By its upper surface, with the Levator palpebrae ; by its under sur- 

 fii'-t\ with the optic nerve, the ophthalmic artery, the nasal nerve, and the branch 

 of the third nerve which supplies it ; and, in front, with the tendon of the Superior 

 oblique and the globe of the eye. 



The Inferior and Internal Recti arise by a common tendon (the ligament of 

 Zinn), 1 which is attached round the circumference of the optic foramen, except at 

 its upper and outer part. The External rectus has two heads : the upper one 

 arises from the outer margin of the optic foramen immediately beneath the Superior 

 rectus ; the lower head, partly from the ligament of Zinn and partly from a small 

 pointed process of bone on the lower margin of 

 the sphenoidal fissure. Each muscle passes Rectus superior. 



forward in the position implied by its name, to Levator 



be inserted by a tendinous expansion (the paipebrce superior, 

 tunica albugined] into the sclerotic coat, about Obiiquu* superior. : 

 three or four lines from the margin of the T. S 5 



cornea. Between the two heads of the Ex- 

 ternal rectus is a narrow interval, through 

 which passes the third, the nasal branch of the 

 ophthalmic division of the fifth and sixth 

 nerves, and the ophthalmic vein. Although 



1 IT c j.1. 1 Keclus inferior. 



nearly all ot these muscles present a common 



orio-in and arp insprtpd in similar manner FIG. 272. The relative position and attach- 

 )n e lrl ment of the muscles of the left eyeball. 



into the sclerotic coat, there are certain differ- 

 ences to be observed in them as regards their length and breadth. The Internal 

 rectus is the broadest, the External is the longest, and the Superior is the thinnest 

 and narrowest. 



The Superior oblique is a fusiform muscle placed at the upper and inner side of 

 the orbit, internal to the Levator palpebrge. It arises about a line above the inner 

 margin of the optic foramen, and, passing forward to the inner angle of the orbit, 

 terminates in a rounded tendon, which plays in a ring or pulley (trochled) formed by 

 fibro-cartilaginous tissue attached to a depression beneath the internal angular pro- 

 cess of the frontal bone, the contiguous surfaces of the tendon and ring being lined 

 by a delicate synovial membrane and enclosed in a thin fibrous investment. The 

 tendon is reflected backward, outward, and downward beneath the Superior rectus 

 to the outer part of the globe of the eye, and is inserted into the sclerotic coat, 

 midway between the cornea and entrance of the optic nerve, the insertion of the 

 muscle lying between the Superior and External recti. 



Relations. By its upper surface, with the periosteum covering the roof of the 

 orbit and the fourth nerve : the tendon, where it lies on the globe of the eye is 

 covered by the Superior rectus; by its undi-r surface, with the nasal nerve and 

 the upper border of the internal rectus. 



The Inferior oblique is a thin, narrow muscle placed near the anterior margin 

 of the orbit. It arises from a depression on the orbital plate of the superior 



1 The ligament of Zinn ought, perhaps more appropriately, to be termed the aponeurosis or tendon 

 of Zinn. Mr. C. B. Lockwood has described a somewhat similar structure on the under surface of the 

 Superior rectus muscle, which is attached to the lesser wing of the sphenoid, forming the upper and 

 outer margin of the optic foramen. This superior tendon gives origin to the Superior rectus, the 

 superior head of the External rectus, and the upper part of the Internal rectus. (Journal of Anatomy 

 and Physiology, vol. xx. part i. p. 1.) 



