CEANIAL NEEVES 245 



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 brain 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 

 lohich lies immediately 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-like 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. 



iii. The mandibular branch, the posterior and 

 smaller of the two, crosses the upper jaw, and 

 then curving round the angle of the mouth, 

 where it lies very close to the surface, runs 

 forwards along the lower jaw. It supplies the 

 muscles moving the lower jaw. 



sixth nerve is very slender, and arises from the 

 ventral surface of the medulla near the median plane, 

 and a short way behind the roots of the fifth and 

 seventh nerves ; it passes out through the same 

 foramen with these nerves, lying below them and 

 separated from them by dense connective tissue. It 

 supplies the rectus externus. 



