THE TRIGEMINAL NERVE 



79 



sensory nucleus of the trigeminal, it may spread to affect the 

 neighbouring grey matter. As a result, pain may be ex- 

 perienced, or hypersesthetic areas may develop, on the side 

 of the neck in areas supplied by C. 2 and 3 (Fig. 69). 



It must also be remembered that, when a "focus of 

 irritation " is established in a sensory nucleus which is related 

 to the sensory nucleus of the trigeminal, the latter may also 

 be stimulated. This explanation accounts for the occurrence 



Facial 

 nerve 



Motor fibres 



FIG. 42. Transverse Section through the Pons (Diagrammatic). 



of pain in the head or face in lesions of the lungs, heart or 

 stomach. The pathological afferent impulses set up a " focus 

 of irritation " in the sensory nucleus of the vagus, and from 

 there they spread to affect the sensory nucleus of the fifth 

 (Fig. 47)- 



The Facial or Seventh Cerebral Nerve consists of a 

 large motor root and a small sensory root which is termed the 

 nervus intcrmcdius (of Wrisberg) The motor root arises in 

 a nucleus, which is situated in the substance of the pons, 



