304 THE MUSCLES AND FASCIA. 



fleshy, and finally terminates in a wide aponeurosis, which is inserted into the 

 upper margin of the superior tarsal plate. From this aponeurosis a thin expan- 

 sion is continued onward, passing between the fibres of the Orbicularis to be 

 inserted into the skin of the lid, and some deeper fibres blend with an expansion 

 from the sheath of the Superior rectus muscle, and are with it prolonged into the 

 conjunctiva. 



Relations. By its upper surface, with the frontal nerve and. supraorbital 

 artery, the periosteum of the orbit and lachrymal gland ; 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 palpebrse, and 

 from the fibrous sheath of the optic nerve ; and is inserted by a tendinous ex- 

 pansion into the sclerotic coat, about three or four lines from the margin of 

 the cornea. 



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

 face, 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 



Rectus superior. ^ ne sphenoidal fissure. Each muscle passes 



Levator forward^m the position implied by its name, to 



.superior. ' ^^ b e inserted- by a tendinous expansion (the 



nparior.j N"^j7fc=^^ tunica albuginedj^nto the sclerotic coat, about 



i s e ^rbes 35 three or four lines from the margin of the 



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 



Rectus inferior. V , , f , . 



nearly all ot these muscles present a common 



FIG. 198. The relative position and attach- :: ^rl rf > inoprtprl in , similar mannpr 



ment of the muscles of the left eyeball. origin ana are inserted m a simile 



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 formed by cartil- 

 aginous tissue attached to a depression beneath the internal angular process 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, 



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 ami 

 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.) 



