82 AN INTRODUCTION TO ZOOLOGY 



capsule. Outside the skull it divides into two branches, the oph- 

 thalmic and the maxillo-mandibular. The ophthalmic branch, 

 which is mainly a sensory nerve, runs forward through the orbit 

 along its inner side, passing above all the eye muscles save the superior 

 rectus. At the anterior end of the orbit it divides into two main 

 branches, one to the mucous membrane of the olfactory organ, and 

 the other to the skin round the snout. The maxillo-mandibular 

 branch is a short mixed nerve that passes outwards just in front of 

 the auditory capsule and soon divides into two branches. Its maxil- 

 lary branch runs forward in the lower part of the orbit below the 

 eyeball and supplies the upper jaw, upper lip, the lower eyelid with 

 its depressor muscle and the adjacent parts. The mandibular 

 branch goes outwards, downwards and backwards beneath the quad- 

 rato-jugal bone to the articulation of the mandible. It passes round 

 this and forward along the outer side of the lower jaw, to which it 

 gives branches supplying the lower lip and skin muscles of the floor 

 of the mouth. The fifth nerve as a whole, then, is a mixed nerve 

 dividing into three main branches, hence its name, the trigeminal. 



The seventh, or facial nerve, is also a mixed nerve, arising from the 

 side of the front end of the medulla, with a distribution somewhat 

 resembling the fifth. Like this, it runs to the pro-otic ganglion and 

 leaves the skull by the same foramen. Outside, it at once divides 

 into two branches, the palatine and the hyomandibular. The 

 palatine runs forward close above the mucous membrane of the mouth 

 in the lower inner part of the orbit. At the front end of the orbit 

 it is joined by a cross piece, an anastomosis, to a twig from the 

 maxillary branch of the fifth nerve. It is distributed to the mucous 

 membrane of the front end of the roof of the mouth. The hyomandi- 

 bular branch proceeds outwards around the auditory capsule, past 

 the inner end of the columella auris, just beyond which it receives 

 an anastomosis linking it with the ninth nerve. Thence it runs 

 downwards in the posterior wall of the Eustachian tube, giving twigs 

 to the tympanum, to the articulation of the mandible to which it 

 sends twigs. Here it divides into two, one branch, the internal 

 mandibular, runs in the floor of the mouth near the lower jaw supply- 

 ing the muscles and skin. The other, the hyoidean, is larger and 

 more posterior and passes forwards in the floor of the mouth by the 

 side of the anterior cornu of the hyoid cartilage, supplying the skin 

 and muscles on its way. 



The auditory nerve, which is the eighth of the series, is a short 

 stout nerve, purely sensory, coming from the side of the medulla 

 just behind the seventh. It passes straight out into the auditory 

 capsule through a special foramen and is distributed to the epithe- 

 lium lining the various parts of the internal ear. 



