906 VISCERAL ANATOMY. 



Others admit a hyaloid membrane surrounding the vitreous, but deny that 



it splits to enclose the lens, and assign but one layer to the suspensory 



ligament, namely, that in front of the Canal of Petit. [Gray, etc.] 

 Describe the Muscles of the Eyeball. They number 6, of which 4 are 

 Recti and 2 Oblique, as follows : 



Rectus Superior,* 1 from the upper margin of the optic foramen and the 



sheath of the optic nerve, into the sclerotic coat. Action, to rotate the 



eyeball upwards. Nerve, 3d cranial. 

 Rectus Inferior,* from the ligament of Zinn, into the sclerotic coat. 



Action, rotates the eyeball downwards. Nerve, 3d cranial. 

 Rectus Internus,^ from the ligament of Zinn, into the sclerotic coat. 



Action, rotates the eyeball inwards. Nerve, 3d cranial. 

 Rectus Externtts, 2 by two heads, the upper from the outer margin of the 



optic foramen, the lower from the ligament of Zinn and a bony process 



FIG. 102. 



at lower margin of the sphenoidal fissure, into the sclerotic coat. 10 

 Action, to rotate the eyeball outwards. Nerve, 6th cranial, or abducens. 

 Between the two heads of the external rectus pass the 3d, nasal branch 

 of the 5th, and the 6th cranial nerves, and the ophthalmic vein. 



Obliquus Superior,' 1 from about a line above the inner margin of the optic 

 foramen, its tendon passing through a "pulley" 12 near the internal an- 

 gular process of the frontal bone and thence beneath the rectus superior, 

 into the sclerotic cqat, at right angles 8 to the insertion of the rectus 

 superior. Action, to rotate the eyeball on its antero-posterior axis. 

 Nerve, 4th cranial, or patheticus. 



Obliquus Inferior* from the orbital plate of the superior maxillary, 

 into the sclerotic coat below the insertion of the external rectus and at 

 right angles thereto. Action,io rotate the eye on its antero-posterior.axis. 

 Nerve, 3d cranial. 



