332 AN INTRODUCTION_ L TO ZOOLOGY 



the turbinal bones. It is purely sensory in function and subserves 

 the sense of smell. Its fibres pass in numerous bundles through the 

 cribriform plate to enter the olfactory bulb. 



The vomero-nasal or septal nerve is a small nerve whose fibres 

 also pass through the cribriform plate and, as just noted, form a 

 plexus with those of the riervus terminalis. 



The optic nerve enters the orbit and runs straight to the eye. 

 It penetrates the sclerotic coat, the choroid coat and the retina, and 

 at the blind spot spreads out radially to be distributed over the 

 internal surface of the retina. It is a purely sensory nerve and sub- 

 serves the function of sight. 



The oculomotor nerve enters the orbit through the foramen 

 lacerum anterius. It is a motor nerve, and breaks up to be dis- 

 tributed to the internal, superior and inferior recti and the inferior 

 oblique muscles of the eye-ball. 



The pathetic or trochlear nerve is also a motor nerve accompany- 

 ing the third into the orbit, but passing across its inner wall to the 

 superior oblique muscle. 



The trigeminal nerve is a very large mixed nerve containing both 

 sensory and motor fibres. A short distance from its origin it swells 

 out to form the large Gasserian ganglion, from which its three main 

 trunks are given off, viz. : the ophthalmic, the maxillary and the 

 mandibular. The first two of these leave the skull by the foramen 

 lacerum anterius, while the last leaves through the anterior portion 

 of the foramen lacerium medium, that is, the portion that in many 

 mammals is a separate aperture, the foramen ovale. 



The ophthalmic trunk is a large nerve which crosses the mesial 

 border of the orbit and, after giving off twigs to the tissues in the 

 region of the eyelid and lachrymal region, reaches the front end of 

 the dorso-mesial wall of the orbit. Here it splits into two branches, 

 the nervus frontalis and the nervus naso-ciliaris. The frontalis 

 goes through the notch at the front end of the supra-orbital process 

 of the frontal bone to the skin and subcutaneous region of the upper 

 eyelid. The naso-ciliaris passes through the internal orbital foramen 

 to the nasal region. 



The second trunk, the maxillary, passes along the inner border of 

 the orbit and the main part of it goes through the infra- orbital canal 

 as the infra-orbital nerve, passing to the front end of the upper lip 

 and the snout, and also giving branches to the anterior teeth. 

 Within the orbit it gives off at the hinder end a subcutaneous branch 

 going outwards to the skin ; a sphenopalatine branch, which after a 

 short distance enlarges to form the sphenopalatine ganglion and the 

 posterior dental nerve going to the hindermost teeth. From the 

 sphenopalatine ganglion are given off several naso-sphenopalatine 



