508 



THE HUMAN BODY. 



foramen through which the optic nerve enters the orbit. In 

 the figure, which represents the orbits opened from above, 

 the superior rectns of the right side has been removed. The 

 superior oblique or pulley (trocUlear) muscle, t, arises behind 

 near the straight muscles and forms anteriorly a tendon, u, 

 which passes through a fibre-cartilaginous ring, or pulley, 

 placed at the notcli in the frontal bone where it bounds 

 superiorly the front end of the orbit. The tendon then turns 



FIG. 141. The eyeballs and their muscles as seen when the roof of the orbit 

 has been removed and ilie fat in the cavity has been partly cleared away. On the 

 right side the superior rectus muscle has been cut away, a, external rectus ; s, 

 superior rectus ; i, internal rectus; /. superior oblique. 



back and is inserted into the eyeball between the upper and 

 outer recti muscles. The inferior oblique muscle does not 

 arise, like the rest, at the back of the orbit, but near its front 

 at the inner side, close to the lachrymal sac. It passes thence 

 outwards and backwards beneath the eyeball to be inserted 

 into its outer and posterior part. 



The inner, upper, and lower straight muscles, the inferior 

 oblique, and the elevator of the upper lid are supplied by 

 branches of the third cranial nerve. The sixth cranial nerve 

 goes to the outer rectus; and the fourth to the superior oblique. 



The eye may be moved from side to side; up or down; 

 obliquely, that is neither truly vertically nor horizontally, 

 but partly both ; or, finally, it may be rotated on its antero- 

 posterior axis. The oblique movements are always accom- 



