THE OPTIC NERVE 



53 



Additional signs may be present and may help in the 

 localisation of lesions producing homonymous hemianopia. 

 Lesions affecting the optic tract are likely to cause some 

 motor paralysis or paresis. The third and fourth cerebral 

 nerves, owing to their proximity, may be involved, while the 



T2 I 3 



FIG. 30. Dissection of Brain, showing the Lateral Aspect of the 

 Internal Capsule. 



i. Internal capsule. 6. Optic nerve. 7. Optic tract. 10. Mid-brain. 



lesion may affect the pyramidal tract, as it descends in the 

 mid-brain in close relation to the optic tract (Fig. 30). 



When the upper neurone fibres are affected in the internal 

 capsule, the adjoining acoustic and sensory fibres (p. 35) are 

 likely to be involved, causing the occurrence of deafness and 

 of irregularly distributed areas of anaesthesia on the opposite 



