THE CRANIAL NERVES. 71 



orbital septum, and is inserted upon the upper suface 

 of the eyeball. 



183. Divide and reflect the superior rectus, looking 

 for the small branch of the third nerve which enters it, 

 and then trace the ophtlialmic nerve through the orbit, 

 pushing aside other parts which come in the way, but 

 not dividing them. 



a. Soon after it enters the orbit, the ophthalmic 

 trunk divides into a larger and smaller branch. 

 The former crosses above the optic nerve and 

 beneath the superior oblique muscle ; in front 

 of the orbit it passes over the Harderian gland, 

 and, on dividing and removing the superior 

 oblique muscle, may be traced forward between 

 the gland and the inner boundary of the orbit 

 till it pierces the latter to enter the nasal 

 chamber. 



b. The smaller or ventral division of the ophthal- 

 mic trunk, turns mesially below the optic nerve, 

 and there enters the ophthalmic ganglion. The 

 ganglion is also joined by a considerable branch 

 from the third nerve, which lies here to the in- 

 ner side of the ophthalmic branch. From the 

 ganglion a number of ciliary nerves run forward 

 to the eyeball. They may be traced by raising 

 and turning forward the optic trunk. 



184. As the ophthalmic nerve enters the eyeball it 

 lies on the external rectus muscle, which arises from 

 the hollow on the inner surface of the base of the skull 

 under the anterior clinoid processes, and passes forward 

 to be inserted on the outer side of the eyeball. Care- 

 4 



