SYPHILITIC MENINGITIS. 163 



dura on the other. The disease, therefore, presents itself as a 

 diffuse gummatous meningo-encephalitis and the resulting cranial 

 nerve paralyses may be associated with symptoms referable to 

 lesions of the crura, pons or medulla. These parts of the cerebro- 

 spinal axis may be compressed by the infiltrated membranes or 

 their nutrient vessels may become occluded and softening result. 

 Under these circumstances various forms of true " crossed- 

 paralysis" may present themselves, the cranial nerve paralysis 

 being on the opposite side to the hemiplegia. Crossed paralysis 

 may also be simulated; the paralysis of the cranial nerve and 

 the hemiplegia being caused by two separate and distinct foci of 

 disease, indeed syphilitic meningitis is characterised by its erratic 

 distribution as well as by its tendency to spontaneous remission 

 and relapse. 



The vertex is sometimes the seat of the disease and the exposure 

 of the head to blows may appear to favour manifestations in this 

 locality. If the meningitis lies over the precentral convolution, 

 Jacksonian epilepsy may be expected. Syphilitic meningitis is, 

 however, most characteristically seen at the base of the brain, 

 especially in the region of the optic chiasma and between the crura 

 cerebri. The relations of the cranial nerves to each other as 

 they lie in the membranes and to the three fossae of the base of 

 the skull are of importance in the diagnosis and localisation 

 of the mischief. The relations which different nerve trunks bear 

 to each other on their course through the membranes to their 

 foramina of exit is in several instances very different from the 

 relations of the nuclei of the same nerves in the cerebro-spinal 

 axis, and thus disease in the meninges may be differentiated from 

 disease within the brain. An accurate knowledge of the relations 

 of the nerves to the different fossae of the skull is of further 

 assistance in localisation of the lesion. 



In the anterior fossa lie the olfactory nerves ; to the middle fossa 

 belong the fifth and sixth nerves, with those above them, except the 

 olfactory ; to the posterior fossa belong the fifth and sixth nerves 

 and those below them. The fifth nerve may be said to lie at the 

 junction of the middle and posterior fossae, its stem of origin 



112 



