354 



HUMAN ANATOMY. 



RECTUS INFERIOR. Origin, from lower and inferior part 

 of optic foramen (ligament of Zinn) ; insertion, into lower sur- 

 face of sclerotic; action, rotates the eyeball downward; nerve, 

 third cranial. 



RECTUS INTERNUS. Origin, same as inferior rectus ; inser- 

 tion, into inner surface of sclerotic; action, rotates the eyeball 

 inward; nerve, third cranial. 



Rl 



Rm, 



FIG. 160. 



The orbital muscles. Lp., levator palpebrse superioris; Os, supe- 

 rior oblique; Rs, superior rectus; Rl, external rectus; Oi, inferior 

 oblique; Ri, inferior rectus; Rm, internal rectus; Tr, trochlea. (Ball.) 



RECTUS EXTERNUS. Origin, by two heads lower, from 

 ligament of Zinn and lower margin of sphenoidal fissure ; upper, 

 from outer margin of optic foramen; insertion, into outer sur- 

 face of sclerotic; nerve, abducens, or sixth cranial. Passing 

 between the two heads are the ophthalmic vein, the third, nasal 

 branch of fifth, and sixth nerves. 



