PHYSIOLOGICAL CLASSIFICATION OF THE CRANIAL NERVES. 609 



Fourth Pair. Patheticus, or trochlearis ; a motor nerve sent to the superior oblique 

 muscle of the eye. 



Fifth Pair. A small motor root (nerve of mastication), distributed to the muscles of 

 mastication, and a large root (trifacial), the nerve of general sensibility of the face. 



Sixth Pair. Motor oculi externus, or abducens ; a motor nerve passing to the exter- 

 nal rectus' muscle of the eye. 



Seventh Pair. Portio mollis, or auditory, a special nerve of hearing; and the portio 

 dura, or facial, a motor nerve distributed to the superficial muscles of the face. 



Eighth Pair. Glosso-pharyngeal ; pneumogastric, or par vaguin; and spinal acces- 

 sory. Three mixed nerves, with quite extensive distributions. 



Ninth Pair. Sublingual, or hypoglossal ; a motor nerve distributed to the tongue. 



Physiological Classification of the Cranial Nerves. 



(a) Nerves of Special Sense. 

 Olfactory. 

 Optic. 

 Auditory. 



Gustatory, comprising a part of the glosso-pharyngeal and a small filament from the 

 facial to the lingual branch of the fifth. 



(b) Nerves of Motion. 



Nerves of motion of the eyeball, comprising the motor oculi communis", the patheti- 

 cus, and the motor oculi externus. 



Nerve of mastication, or motor root of the fifth. 

 Facial, sometimes called the nerve of expression. 

 Spinal accessory. 

 Sublingual. 



(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 according 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 endowed with general sensi- 

 bility; and, with the exception of the gustatory nerves, they do not present a ganglion 

 on their roots, in this, also, differing from the ordinary sensory nerves. They are capa- 

 ble, therefore, of conveying to the nerve-centres only certain peculiar impressions; such 

 as odors, for the olfactory nerves; light, for the optic nerves; and sound, for the auditory 

 nerves. The proper transmission of these impressions, however, involves the action of 

 accessory organs, more or less complex ; and we shall 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 the movements of the iris, 

 upon which the results of experiments are somewhat contradictory. As an introduction 

 to the study of the functions of this nerve, it will be necessary to describe its anatomical 

 relations. 



39 



