CHAP. XX.] THE QLOSSO-PHARYNGEAL NERVE. 115 



of the lips constitutes it a pre-eminently sensitive nerve of touch, 

 in those regions. 



The study of the pathological conditions of this nerve illustrates 

 its physiology in a highly interesting manner. In the dentition of 

 children, whether primary or secondary, it is always affected, more 

 or less : and in excitable states of the nervous centres, the irritation 

 of it consequent upon the pressure of the teeth often gives rise to 

 convulsions, the brain and spinal cord being irritated ; and we can 

 often trace to such irritation, whether in infancy or in childhood, 

 the foundation of epileptic seizures in subsequent years. Painful 

 affections of the face (neuralgia) have their seat in this nerve; tic- 

 douloureux for example. Many of the instances of painful affection 

 of this nerve or of branches of it, which come under our observation, 

 are well marked examples of reflected sensation, the primary irrita- 

 tion being conveyed to the centre by the vagus or the sympathetic 

 from the stomach or intestinal canal. No one of these is so common 

 as the pain over the brow, which so often follows derangement of 

 stomach digestion ; and which may frequently be instantaneously 

 removed by taking away the source of irritation, as by neutralizing 

 free acid in the stomach. Frequently also the branches of this 

 nerve, in greater or less number, on one or both sides, may, accord- 

 ing to the humoral view, form a focus of attraction for a morbific 

 matter generated in the blood, in persons exposed to the paludal 

 poison, or in persons of rheumatic or gouty constitution ; in these 

 cases, as in most others of similar pathology, the neuralgia occurs 

 in paroxysms of greater or less severity, each paroxysm being fol- 

 lowed by a period of convalescence, which lasts, it may be supposed, 

 until the morbid matter has been again accumulated in quantity 

 sufficient to induce a high degree of irritation of the nerves. 



Of the Eighth Pair of Nerves. We must examine separately the 

 anatomy and physiology of each of the three nerves which taken 

 together constitute the eighth pair ; and first, 



Of the Glosso-pharyngeal. This nerve consists of several small 

 fascicles of fibres, which lie close together, and are implanted in the 

 upper part of the medulla oblongata behind the olivary body. The 

 fibres penetrate to the centre of the medulla (the olivary columns) 

 where they connect themselves with a special accumulation of vesi- 

 cular matter. 



The glosso-pharyngeal nerve escapes through a small foramen in 

 the dura mater, at the anterior part of the foramen lacerum pos- 

 terius. Immediately after it has passed this foramen, a small gan- 

 glion which involves only some of the fibres of the nerve, is formed 



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