126 NERVOUS SYSTEM. 



(b.) Nerves of Motion. 



Nerves of motion of the eyeball; comprising the motor 

 oculi communis, the patheticus, and the motor oculi externus. 

 Nerve of mastication, or motor root of the fifth. 

 Facial, sometimes called the nerve of expression. 

 Spinal accessory. 

 Sublingnal. 



(c.) Nerves of General Sensibility. 



Trifacial, or large root of the fifth. 

 A portion of the glosso-pharyngeal. 

 Pneumogastric. 



In the above arrangement, the nerves are classified ac- 

 cording to their properties at their roots. In their course, 

 some of these nerves become mixed, and their branches are 

 both motor and sensory, such as the pneumogastric and the 

 inferior maxillary branch of the trifacial. 



The nerves of special sense are but slightly, if at all, en- 

 dowed with general sensibility ; and, with the exception of 

 the gustatory nerves, do not present a ganglion on their 

 roots, in this, also, differing from the ordinary sensory 

 nerves. They are capable, therefore, of conveying to the 

 nerve-centres only certain peculiar impressions, such as 

 odors, for the olfactory nerves ; light, for the optic nerves ; 

 sound, for the auditory nerves. The proper transmission of. 

 these impressions, however, involves the action of accessory 

 organs, more or less complex ; and we will pass over the 

 properties of these nerves until we come to treat in full of 

 the special senses. 



Motor Oculi Communis (Third Nerve). 



The third cranial nerve is the most important of the 

 motor nerves distributed to the muscles of the eyeball. Its 

 physiology is readily understood in connection with its dis- 

 tribution, the only point at all obscure being its relations to 



