THE ORBIT 249 



i. The rectus superior runs outwards and forwards 

 to be inserted into the dorsal surface of the 

 eyeball. 



ii. The rectus internus, or anterior, runs forwards 

 between the skull-wall and the eyeball, and is 

 inserted into the anterior surface of the latter. 



iii. The rectus externus, or posterior, is the hind- 

 most of the eye-muscles, and runs directly 

 outwards behind the eyeball, to be inserted 

 into its posterior surface. 



iv. The rectus inferior runs outwards and forwards 

 beneath the eyeball, and is inserted into its 

 ventral surface. 



The origin of the rectus inferior can be seen from above, 

 between the other recti muscles ; to see its insertion, turn the 

 eyeball up. 



b. The oblique muscles are two in number. They 

 arise close together at the anterior end of the 

 orbit, and run backwards and outwards to the 

 eyeball. 



i. The obliquus superior is inserted into the dorsal 

 surface of the eyeball, just in front of the in- 

 sertion of the rectus superior. 



ii. The obliquus inferior is inserted into the ventral 

 surface of the eyeball, just in front of the in- 

 sertion of the rectus inferior. 



To see the obliquus inferior, turn the eyeball up. 



C. The Cranial Nerves. 



These should be dissected before the brain is removed, in 

 order that their entire course may be seen. 



Dissect the nerves on the right side, leaving the left side 

 for the dissection of the sense-organs. 



The ophthalmic branches of the fifth and seventh nerves, 

 which run through the orbit close to the skull-wall, and dorsal 

 to all the eye-muscles, should be identified at once ; and care 

 m/iist be taken not to injure them. 



