THE ORBIT 



249 



handle of the knife can be introduced into the space between it 

 and the eyeball. In favourable cases the extent of the fascia 

 can be gauged, and perhaps even the prolongations or sheaths 

 which it gives to the tendons of the ocular muscles may be 

 made out. The description of the fascia bulbi is given on p. 259. 



Musculus Rectus Superior. The superior rectus, which lies 

 under cover of the levator palpebrse superioris, is now fully 

 exposed. It is the thinnest of the recti muscles, and it arises 

 from the upper margin of the optic foramen, passes forwards 

 above the optic nerve, and ends, upon the upper aspect of 

 the eyeball, in a thin, delicate 

 and somewhat expanded 

 tendon, which is inserted 

 into the sclera, about 8 mm. 

 posterior to the sclero-cor- 

 neal junction. It is supplied 

 by a branch from the sup- 

 erior division of the oculo- 

 motor nerve ; when it con- 

 tracts it turns the eyeball so 

 that the centre of the cornea 

 moves up wards and medially. 



Musculus Obliquus Sup- 

 erior. The Superior oblique 

 muscle is the longest and 



5 



narrowest of the muscles 

 attached to the eyeball. 

 It arises from the roof of the orbit, immediately anterior 

 to the upper and medial part of the optic foramen between 

 the rectus superior and the rectus medialis. It passes 

 forwards along the upper part of the medial wall of the 

 cavity, above the medial rectus. At the anterior part of 

 the orbit it ends in a slender tendon, which enters the trochlea 

 and at once changes its direction, proceeding backwards and 

 laterally, upon the upper surface of the eyeball, under cover 

 of the superior rectus. Beyond the lateral edge of the 

 superior rectus the tendon expands somewhat, and is inserted 

 into the sclera, midway between the entrance of the optic 

 nerve and the cornea (Fig. 93). 



The trochlea or pulley through which the tendon passes is 

 a small fibre-cartilaginous ring, which is attached by fibrous 

 tissue to the trochlear fossa of the frontal bone. The pulley 



G. 93- Diagram of the Superior 



bli i u< : Muscle " < From 



Meyer. 



_, ,. . 



a. Trochlea and synovia! sheath. 



