CHAPTEE IV. 



SPINAL NERVES MOTOR NERVES OF THE EYEBALL. 



Special nerves coming from the spinal cord Cranial nerves Anatomical classi- 

 fication Physiological classification Motor oculi communis (third nerve) 

 Physiological anatomy Properties and functions Influence upon cer- 

 tain muscles of the eyeball Action of the inferior oblique muscle Influ- 

 ence upon the movements of the iris Patheticus, or trochlearis (fourth 

 nerve) Physiological anatomy Properties and function Action of the 

 superior oblique muscle Motor oculi externus, or abducens (sixth nerve) 

 Physiological anatomy Properties and function. 



Spinal Nerves. 



WITH a thorough knowledge of the general properties of 

 the nerves belonging to the cerebro-spinal system, the func- 

 tions of most of the special nerves are apparent simply from 

 their anatomical relations. This is especially true of the 

 spinal nerves; which, in general terms, are distributed to 

 the muscles of the trunk and extremities, the sphincters, 

 and' to the integument covering these parts, the posterior 

 segment of the head, and a portion of the mucous mem- 

 branes. It is evident, therefore, that an account of the 

 exact function of each nervous branch would necessitate a 

 full description, not only of the nerves, but of the muscles 

 of the body, which is manifestly within the scope only of 

 elaborate treatises on descriptive anatomy. It is sufficient 

 to indicate, in this connection, that there are thirty-one pairs 

 of spinal nerves \ eight cervical, twelve dorsal, five lumbar, 

 five sacral, and one coccygeal. Each nerve arises from the 

 spinal cord by an anterior (motor) and a posterior (sensory) 



