1022 ORGANS OF THE SENSES AND Tl 



WUMENT 



Whitnall 1 has pointed out that the upper part of the sheath of the Levator palpebrse becomes 

 thickened in front and forms, above the anterior part of the muscle, a transverse ligamentous 

 band which is attached to the sides of the orbital cavity. On the medial side it is mainly fixed 

 to the pulley of the Obliquus superior, but some fibers are attached to the bone behind the pulley 

 and a slip passes forward and bridges over the supraorbital notch; on the lateral side it is fixed 

 to the capsule of the lacrimal gland and to the frontal bone. In front of the transverse ligament- 

 ous band the sheath is continued over the aponeurosis of the Levator palpebrse, as a thin con- 

 nective-tissue layer which is fixed to the upper orbital margin immediatly behind the attach- 

 ment of the orbital septum. When the Levator palpebrse contracts, the lateral and medial parts 

 of the ligamentous band are stretched and check the action of the muscle; the retraction of the 

 upper eyelid is checked also by the orbital septum coming into contact with the transverse part 

 of the ligamentous band. 





FIG. 889. Muscles of the right orbit. 



The four Recti (Fig. 889) arise from a fibrous ring (annulus tendineus communis) 

 which surrounds the upper, medial, and lower margins of the optic foramen and 

 encircles the optic nerve (Fig. 890) . The ring is completed by a tendinous bridge 

 prolonged over the lower and medial part of the superior orbital fissure and attached 

 to a tubercle on the margin of the great wing of the sphenoid, bounding the fissure. 

 Two specialized parts of this fibrous ring may be made out: a lower, the ligament 

 or tendon of Zinn, which gives origin to the Rectus inferior, part of the Rectus in- 

 ternus, and the lower head of origin of the Rectus lateralis; and an upper, which 

 gives origin to the Rectus superior, the rest of the Rectus medialis, and the upper 

 head of the Rectus lateralis. This upper band is sometimes termed the superior 

 tendon of Lockwood. Each muscle passes forward in the position implied by its 

 name, to be inserted by a tendinous expansion into the sclera, about 6 mm. from the 

 margin of the cornea. Between the two heads of the Rectus lateralis is a narrow 

 interval, through which pass the two divisions of the oculomotor nerve, the naso- 

 ciliary nerve, the abducent nerve, and the ophthalmic vein. Although these 

 muscles present a common origin and are inserted in a similar manner into the 

 sclera, there are certain differences to be observed in them as regards their length 

 and breadth. The Rectus medialis is the broadest, the Rectus lateralis the longest, 

 and the Rectus superior the thinnest and narrowest. 



The Obliquus oculi superior (superior oblique) is a fusiform muscle, placed at the 

 upper and medial side of the orbit. It arises immediately above the margin of the 

 optic foramen, above and medial to the origin of the Rectus superior, and, passing 

 forward, ends in a rounded tendon, which plays in a fibrocartilaginous ring or pulley 

 attached to the trochlear fovea of the frontal bone. The contiguous surfaces of 

 the tendon and ring are lined by a delicate mucous sheath, and enclosed in a thin 



1 Journal of Anatomy and Physiology, vol. xlv. 



