THE RABBIT 303 



the outer side of the eyeball, parallel to the margin of the cornea, 

 and is the inferior oblique. It is inserted in the outer surface of 

 the eyeball near the cornea and passes ventrally beneath the eye- 

 ball to its origin in the anterior surface of the orbit. Immediately 

 beneath the inferior oblique is the insertion of the inferior rectus 

 muscle, which passes posteriorly along the ventral side of the eye- 

 ball to the hinder part of the orbit ; the nerve running along the 

 anterior border of this muscle is the oculomotor nerve. Inserted 

 in the eyeball just back of the inferior oblique is a broad muscle 

 which passes straight back to the hinder part of the orbit ; this is 

 the external (posterior) rectus muscle. Note its relation to the 

 lachrymal gland ; note also the abducens nerve against its inner 

 surface. Above the inferior rectus is the insertion of the internal 

 (anterior) rectus, which extends from the dorsal margin of the 

 eyeball back to the inner wall of the orbit. Inserted in the dorsal 

 wall of the eyeball are two muscles, the superior oblique and 

 superior rectus muscles. The tendon of the former lies at right 

 angles to that of the latter and passes toward the dorsal margin 

 of the inner side of the orbit and through a fibrous loop ; here its 

 direction is changed, and it goes to the body of the muscle, which 

 lies against the medial side of the eyeball. The superior rectus 

 muscle arises in the hinder part of the orbit and passes straight 

 forward to its insertion in the dorsal surface of the eyeball ; lying 

 over the outer surface of this muscle and parallel with it is the 

 delicate levator muscle, which passes to the upper eyelid. Its 

 function is to raise the eyelid. The four heads of the retractor 

 muscle are inserted in the eyeball around the optic nerve. 



Two nerves lie against the medial wall of the orbit ; the lower 

 one is the trochlear, which innervates the superior oblique muscle, 

 and the upper one is a branch of the ophthalmic branch of the 

 trigeminus nerve which passes to the upper eyelid. 



Exercise 28. Draw a diagram showing the eyeball and its muscles 

 and nerves, so far as observed. 



Pull the eyeball forward and cut the optic nerve and the mus- 

 cles. Remove the eyeball from the orbit and cut away the muscles 

 and fat still attached to it. It will be seen to be a spherical struc- 



