494 NERVOUS SYSTEM 



sacral, forming the lumbo-sacral nerve, and enter into the sacral plexus. 

 The upper three anterior sacral nerves, with a branch from the fourth, 

 form the sacral plexus. The greatest portion of the fourth anterior 

 sacral is distributed to the pelvic viscera and the muscles of the anus. 

 The fifth anterior sacral and the coccygeal are distributed to parts 

 about the coccyx. 



The posterior branches of the spinal nerves are quite simple in their 

 distribution. With one or two exceptions, of no great physiological 

 importance, these nerves pass backward from the main trunk, divide 

 into two branches, external and internal, and their filaments of distri- 

 bution go to the muscles and to integument behind the spinal column. 



It is further important to note that all the cerebro-spinal nerves 

 anastomose with the sympathetic. 



CRANIAL NERVES 



Many of the cranial nerves are peculiar, either as regards their 

 general properties or in their distribution to parts concerned in special 

 functions. In some of these nerves, the most important facts con- 

 cerning their distribution have been ascertained only by physiological 

 experimentation, and their anatomy is inseparably connected with their 

 physiology. It would be desirable, if it were possible, to classify these 

 nerves with reference strictly to their properties and uses ; but this can 

 be done only to a certain extent. The common classification of the 

 cranial nerves is the arrangement 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 CRANIAL 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 lingual branch 

 of the fifth pair. 



Nerves of Motion 



Nerves of motion of the eyeball, comprising the motor oculi com- 

 munis (third pair), the patheticus (fourth pair), and the motor oculi 

 externus (sixth pair). 



