242 THE DOG-FISH 



The origin of the rectus inferior cam, he 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 eyebaiU 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, twn the eyeball wp. 



C. The Cranial Herves. 



These should be dissected before the brain is removed, in 

 order that their entire course may be displayed. 



Dissect the nerves on the right side, lea/ving the left side 

 for the dissection of the sense-organs. 



The ophthalndc branches of the fifth and seventh nerves, 

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

 to all the 'eye-rrmscles, should be identified at once; and ca/re 

 must be taken not to injure them. 



1. The olfactory nerves arise on each side in two large 



bundles from the anterior surface of the olfactory 

 lobe, and pass at once through . the siev«-like mem- 

 brane separating the cranial cavity from the nose. 

 They end in the folds of the large olfactory organ. 



Dissect the olfactory nerves from the dorsal surface, taking 

 care to preserve the ophthalmic branches of the fifth and 

 seventh nerves, which run forwards across the olfactory lobe, 

 but separated from it by the cartilaginous cranium. 



2, The optic nerve enters the orbit through a foramen in 



the side- wall of the skuU, near the ventral surface, . 

 and about midway between the origins of the recti 



