FACIAL NERVE. 199 



and second division of the fifth. Thus is explained the fact that 

 a lesion of the petrosal nerve has abolished taste on the anterior 

 part of the tongue. 



The taste fibres from the posterior part of the tongue and the 

 circumvallate papillae travel up in the glossopharyngeal nerve, 

 but leave this by the tympanic branch, and, running in the small 

 superficial petrosal nerve, travel by way of the otic ganglion into 

 the third division of the fifth. (Fig. 18.) 



Within the pons the taste fibres are separate from the com- 

 mon sensory fibres of the fifth, and by some unknown path reach 

 the internal capsule of the opposite side, finally terminating in a 

 taste centre at the tip of the temporo-sphenoidal lobe. 



Another description of the peripheral course of the taste fibres 

 is given by Edinger. According to this writer the terminal nucleus 

 of taste is a mass of grey matter, which has the same vertical 

 extent as the sensory nucleus of the fifth, and which receives 

 afferent fibres in succession from the glossopharyngeal nerve, 

 through its petrous ganglion ; the chorda tympani, through the 

 geniculate ganglion of the facial, and the portio intermedia ; and 

 the lingual nerve, through the Gasserian ganglion. 



FACIAL PARALYSIS AND FACIAL SPASM. 



The facial, like other cranial nerves, may be paralysed by 

 supranuclear, nuclear, or intranuclear lesions. 



A supranuclear lesion may involve the cortex or the con- 

 ducting fibres from the cortical centre to the facial nucleus. 

 The lower end of each ascending frontal convolution is connected 

 with the opposite facial nucleus by fibres which traverse the 

 genu of the internal capsule and pass along the base of the crus. 

 In the crus the facial fibres are immediately internal to the 

 innermost fibres of the pyramidal system, following the general 

 rule that the fibres which decussate first lie nearest to the mid 

 line of the body. 



The cortical centres for articulatory movements of the tongue 

 and movements of the larynx lie in the lowermost part of the 



