252 THE DOG-PISH 



a. The fifth or trigeminal nerve has three main 

 branches, 

 i. The ophthalmic branch arises from the anterior 

 border of the root of the nerve, close to the 

 brain. It runs forwards and upwards for 

 about a quarter of an inch within the skull, 

 and then perforates the skull-wall to enter 

 the orbit, above and a little in front of the 

 origins of the recti muscles. 



In the orbit it runs forwards close to the 



skull- wall, alongside of and immediately below 



the ophthalmic branch of the seventh nerve, 



and dorsal to all the eye-muscles. At the 



anterior and ianer angle of the orbit it passes 



through a canal between the olfactory capsule 



and the cranium, crosses the olfactory lobe, 



and continuing its course straight forwards 



divides into branches, which supply the mucous 



canals of the dorsal surface of the snout. 



Gently press away the train from the skull to see the root 



and the part of the nerve within the cranium, taking care not 



to confound it with the ophthalmic branch of the seventh nerve 



which lies immedAately dorsal to it. In the orbit dissect from 



the side, and in front of the orbit from above. 



The main stem of the fifth nerve on entering 

 the orbit runs forwards and outwards across its 

 floor as a broad riband-Uke band, easily mistaken 

 for a muscle. Near the outer margin of the orbit 

 this divides into the maxillary and mandibular 

 branches. 

 Turn the eye up ; trace the nerve across the floor of the 

 orbit, and follow its branches to their distribution. 



ii. The maxillary branch, which is the anterior 

 and larger of the two, turns over the upper 

 jaw at the anterior border of the orbit, and 

 divides into branches which run forwards 

 to supply the mucous canals of the under 

 surface of the snout. 



