62 



THE NERVOUS SYSTEM 



of the spino-thalamic tract. The condition is termed alternate 

 hemi-ancesthesia, and it may or may not be accompanied by 

 homo-lateral facial paralysis (p. 86). 



The small motor and the large sensory roots emerge side by 

 side from the lateral part of the pons near its upper border, 

 and run laterally through the subarachnoid space before they 

 pierce the dura mater at the apex of the petrous part of the 

 temporal bone (Fig. 35). The acoustic (auditory) nerve, as 



Facial 

 nerve 



~~ Motor fibres 

 FIG. 34. Transverse Section through the Pons (Diagrammatic). 



it passes from the internal acoustic meatus to the pons, lies a 

 little below the trigeminal. Paralysis of the fifth, with signs 

 of cerebellar disease, and with or without symptoms of deaf- 

 ness, is diagnostic of tumour in the neighbourhood of the 

 cerebello-pontine angle (p. 22). 



The SEMI LUNAR (GASSERIAN) GANGLION, which corre- 

 sponds to the ganglion on the posterior root of a spinal 

 nerve, is placed on the sensory root of the trigeminal as it lies 

 on the anterior part of the petrous temporal. It lies immedi- 

 ately postero-lateral to the cavernous sinus and receives 



