280 THE DOG-FISH. 



To see the root, which is large, 'press the brain away from 

 the skull. The dissection is the same as for the corresponding 

 branch of the fifth nerve. 



The main stem of the seventh nerve enters 

 the orbit immediately behind the fifth, and 

 divides almost at once into three main branches. 

 Turn the eye up and dissect the nerve from the side, fol- 

 lowing the branches to their distribution. 



ii. The buccal branch arises from the brain along 

 with the ophthalmic. It accompanies the 

 maxillary branch of the fifth nerve, lying be- 

 tween this and the mandibular branch on the 

 floor of the orbit. It supplies the sensory am- 

 pullae and the sensory canal of the infra-orbital 

 region. This nerve is better seen in the skate. 



iii. The palatine branch is a slender nerve which 

 runs forwards and outwards across the floor 

 of the orbit, immediately behind the main 

 stem of the fifth nerve : it then turns for- 

 wards beneath this nerve and runs along the 

 upper jaw, sending branches to the roof of 

 the mouth. 



iv. The hyoidean or post-spiracular branch is a 

 much stouter nerve, which runs straight 

 outwards along the posterior wall of the orbit 

 towards the spiracle. Continuing its course 

 outwards and backwards, in close contact 

 with the anterior wall of the auditory capsule, 

 it passes along the posterior border of the 

 spiracle, where it lies just beneath the skin, 

 and then runs downwards and backwards 

 along the anterior border of the hyoid arch, 

 giving off an external mandibular branch to 

 the ampullae and sensory canals of the hyo- 

 mandibular region. 



Close to its origin it gives off a number of 

 small * pre-spiracular ' branches, one or more 



