540 



NERVOUS SYSTEM. 



FIG. 193. Roots of tl 



al nerves (Hirschfeld). 



I. Olfactory. 

 II. Optic. ' 



III. Motor oculi communis. 



IV. Patheticus. 



V. Nerve of mastication and trifacial. 

 VI. Motor oculi externus. 

 VII. Facial. 

 VIII. Auditory. 

 IX. Glosso-pharyngeal. 

 X. Pneumogastric. 

 XI. Spinal accessory. 

 XII. Sublingual. 



The numbers 1 to 15 refer to branches which will be de- 

 scribed hereafter. 



Spinal accessory. (Eleventh pair.) 

 Sublingual. (Twelfth pair). 



ment of Sommerring, in which the 

 nerves are numbered from before 

 backward, in the order in which 

 they pass out of the skull, making 

 twelve pairs. 



CLASSIFICATION OF THE CRANI- 

 AL NERVES. 



Nerves of Special Sense. 

 Olfactory. (First pair.) 

 Optic. (Second pair.) 

 Auditory. (Eighth pair.) 

 Gustatory, comprising a part 

 of the glosso-pharyngeal (ninth 

 pair) and a small filament from 

 the facial (seventh pair) to the lin- 

 gual branch of the fifth pair. 



Nerves of Motion. 



Nerves of motion of the eye- 

 ball, comprising the motor oculi 

 communis (third pair), the pathet- 

 icus (fourth pair), and the motor 

 oculi externus (sixth pair). 



Nerve of mastication, or motor 

 root of the fifth pair. 



Facial, sometimes called the 

 nerve of expression. (Seventh 

 pair.) 



Nerves of General Sensibility. 



Trifacial, or large root of the fifth pair. 



A portion of the glosso-pharyngeal. (Ninth pair.) 



Pneumogastric. (Tenth pair.) 



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 pneumo- 

 gastric and the inferior maxillary branch of the trifacial. 



The nerves of special sense have little or no general sensibility ; 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 capable of conveying to the nerve-centres only certain peculiar impres- 

 sions, such as odors, for the olfactory nerves, light, for the optic nerves, and 



