Chap. XIX] THE NERVOUS SYSTEM 395 



also leads to a defect of speech." (Woolsey, " Applied Surgical 

 Anatomy.") 



Association areas. — Those parts of the cerebral cortex which are 

 not the location of special centres are called association areas. 

 It is here that the information received by the various sense centres 

 is built up and coordinated into concepts or perceptions. The 

 various parts of the association areas are connected with the 

 sense centres by means of association fibres. The localization of 

 function in the association areas is not yet determined. 



THE CRANIAL NERVES 



The cranial nerves consist of twelve pairs. They each have a 

 superficial and a deep origin. The superficial origin is the point 

 where they emerge from the under surface of the cerebrum and the 

 medulla, but they can be traced back to various centres in the 

 higher part of the brain, and these centres constitute their deep 

 origin. 



Classification. — The cranial nerves are of three varieties : 

 (1) sensory nerves, (2) motor nerves, and (3) mixed nerves or 

 those containing both sensory and motor fibres. Many of the 

 cranial nerves arise from several nerve-centres, and therefore con- 

 sist of several bundles of nerve-fibres. After these nerves leave 

 the cranium they split up into branches that are widely distrib- 

 uted. 



Numbers and names. — They are named numerically according 

 to the order in which they arise from the brain. Other names 

 are also given to them, derived from the parts to which they are 

 distributed or from their functions. Taken in their order from 

 before backward, they are as follows : — 



1. Olfactory (sensory). 



2. Optic (sensory). 



3. Motor oculi (motor). 



4. Pathetic, or trochlear (motor). 



5. Trifacial, or trigeminal (mixed, but mainly sensory). 



6. Abducens (motor). 



7. Facial (motor). 



8. Auditory (sensory). 



9. Glossopharyngeal (mixed). 



10. Pneumogastric, or vagus (mixed). 



