164 CLINICAL APPLIED ANATOMY. 



from the pons belongs to the fore part of the posterior fossa, 

 whilst the Gasserian ganglion and the three subdivisions of the 

 nerve belong to the middle fossa. 



In the middle fossa the third, fourth and sixth nerves may be 

 involved where they are concentrated in the cavernous sinus or 

 at the sphenoidal fissure, and in such case the optic nerve is also 

 involved as a rule. Affection of the optic chiasma may cause 

 hemianopia. 



The fifth nerve may be picked out by itself as also may one of 

 the ocular nerves. Since the sixth nerve where it pierces the 

 dura is nearer to the fifth than to any other cranial nerve the 

 two may suffer together. 



In the posterior fossa the fifth and seventh nerves may be para- 

 lysed together ; or the fifth with the ninth, tenth, eleventh and 

 twelfth ; or the seventh and eighth. Paralysis of the vago-accessory 

 and hypoglossal nerves, producing unilateral paralysis of palate, 

 tongue and soft palate, is also characteristic of a lesion at the 

 base, outside the medulla and in the region of the jugular and 

 hypoglossal foramina. Or the hypoglossal nerve and the spinal 

 portion of the spinal accessory nerve may be damaged in the 

 membranes near the foramen magnum, producing an associated 

 paralysis of the trapezius, sterno-mastoid and corresponding half 

 of the tongue. 



Special combinations of nerves pointing to basic as opposed to 

 pontine lesions are fifth and sixth, seventh and eighth, eleventh 

 and twelfth. The nuclei of origin of these pairs of nerves are 

 more widely separated than their trunks are where they lie at the 

 base of the brain. But the intimate relation of the seventh and 

 eighth nerves in the petrous bone renders exclusion of disease 

 of the ear necessary before the inference of a meningeal affection 

 is drawn from their associated paralysis. 



CEREBRAL HAEMORRHAGE. 



The corpus striatum and its immediate neighbourhood are by 

 far the most common situations of haemorrhage into the substance 



