194 CLINICAL APPLIED ANATOMY. 



consequently paralysis of the sixth nerve, i.e., of the external 

 rectus, has no great localising valve. 



In the cavernous sinus the third, fourth and sixth nerves 

 have come together, and are associated with the first division 

 of fifth. A lesion in this region may involve all the nerves 

 mentioned, necessarily on one side only. Thrombosis of the caver- 

 nous sinus, growths of the pituitary body, or aneurysms of the 

 intracranial part of the internal carotid, are lesions possible here. 



At the sphenoidal fissure the same nerves are close together 

 and the optic nerve adjacent. A basic meningitis or a perios- 

 titis may involve them all. 



In the orbit the same nerves may be involved by cellulitis, 

 wounds, or rarely growths. In such cases proptosis may be 

 associated, but this may also result from cavernous sinus 

 thrombosis. 



If defects of vision are associated with ocular paralyses the 

 nature of the defect should be ascertained. A lateral homony- 

 mous hemianopia points to a lesion of the optic tract behind 

 the chiasma, i.e., in the region of the crus or the pulvinar. 

 Bitemporal hemianopia indicates a lesion in the chiasma 

 region. 



THE FIFTH NERVE. 



The fifth being a mixed nerve, both motor and sensory 

 symptoms may result when it is either irritated or paralysed. 

 The sensory fibres, after entering the pons, end in the sub- 

 stantia gelatinosa Eolandi, and in an expanded terminal portion 

 of this structure which is known as the sensory nucleus. The 

 cells of termination of the sensory part of the nerve form a 

 column of considerable vertical extent which reaches from the 

 level of the middle cerebellar peduncle to that of the second 

 cervical nerve. (Fig. 17, p. 191.) The whole of this long 

 column is very unlikely to be affected by disease within the pons, 

 and, as a rule, complete anaesthesia in the territory of the fifth is 

 due to a lesion of the collected sensory fibres as they lie in the 

 issuing nerve root. 



