NINTH, TENTH AND ELEVENTH NEEVES. 207 



pressure on the adjacent fillet, such as might occur from quadri- 

 geminal tumours or enlargement of the pineal body, will be 

 associated with defects in the movements of the eyes and other 

 symptoms referable to the corpora quadrigemina. 



Deafness from involvement of the auditory tract in the pons is 

 rare, probably because lesions of the pons usually occur in the 

 tegmental or dorsal region, whilst the auditory tract lies lateral 

 in the lateral fillet and ventral in the corpus trapezoides. The 

 occurrence of paralysis of other cranial nerves which arise from 

 the pons and of opposite hemiplegia will localise the lesion 

 sufficiently. 



THE GLOSSOPHARYNGEAL, VAGUS, BULBAR AND SPINAL 

 ACCESSORY NERVES. 



From both the anatomical and the clinical points of view the 

 glossopharyngeal, vagus and bulbar portion of the spinal accessory 

 nerves are best considered together as forming parts of one large 

 nerve. The fibres are mixed, some being afferent or sensory, 

 and others efferent or motor in function. 



Unilateral lesions of the motor cortex or motor tracts above 

 the motor nucleus of the nerve do not produce any appreciable 

 paralysis of the larynx, pharynx or palate to which the nerve is 

 distributed, but if both cortical centres or supranuclear tracts be 

 damaged a condition known as pseudo-bulbar paralysis is induced. 

 Hence the inference that the bulbar nucleus is connected with 

 each hemisphere of the brain. 



The motor fibres arise from the nucleus ambiguus which 

 extends from the level of the highest issuing roots of the glosso- 

 pharyngeal down to the point of decussation of the fillets which is 

 a short distance above the decussation of the pyramids. (Fig. 17, 

 p. 191.) From this nucleus the motor fibres for the larynx, pharynx 

 and soft palate arise, consequently it has been terra ed the nucleus 

 of phonation and deglutition. The unity of the nucleus explains 

 the combination of paralyses met with in bulbar palsy, i.e., of 

 larynx, soft palate and pharynx, to which may be added paralysis 

 of the tongue and lips if the hypoglossal nucleus is also affected. 



