556 THE CKANIAL NERVES. 



inner surface of the fauces and pharynx. This contact produces an im- 

 pression which is conveyed by the glossopharyngeal nerve inward to the 

 medulla oblongata, whence it is reflected outward in the form of a motor 

 impulse. The sensibility which, by the contact of masticated food or 

 nutritious liquids, thus produces the movements of swallowing, if sub- 

 jected to the influence of nauseous or irritating substances, will cause an 

 inverted muscular reaction, equally involuntary in character. 



Natural stimulants, therefore, applied to the mucous membrane of the 

 pharynx, excite deglutition; unnatural stimulants excite vomiting. If 

 the linger be introduced into the fauces and pharynx, or if the mucous 

 membrane of these parts be irritated by tickling with the end of a 

 feather, the sensation of nausea, conveyed through the glossopharyngeal 

 nerve, is sometimes so great as to produce immediate vomiting. This 

 method may be employed in cases of poisoning, when it is desirable to 

 excite vomiting rapidly, and when emetic medicines are not at hand. 



Motor Properties of the Glossopharyngeal. Although this nerve is 

 shown, by the result of observation, to be exclusively sensitive at its 

 origin, it is found, if examined outside the cavity of the cranium, to 

 possess motor properties. In the experiments of Herbert Mayo upon 

 the ass, confirmed by those of Longet on the horse and the dog, irritation 

 of this nerve in the neck produced contraction in the stylopharyngeal 

 muscles and in the upper part of the pharynx. These movements were 

 not the result of reflex action, but were excited through the nerve from 

 within outward; since, in the experiments of Longet, they were called 

 out after the nerve had been divided, by applying the irritation to its 

 peripheral extremity. 



The glossophaiyngeal, therefore, after its exit from the jugular fora- 

 men, is a mixed nerve. In addition to its own original sensitive fila- 

 ments, it has received a branch of communication from the facial which 

 is undoubtedly of a motor character, and also a branch from the pneu- 

 mogastric. The pneumogastric branch is also regarded, on anatomical 

 grounds, as really made up, wholly or in part, of motor fibres derived 

 from the spinal accessory, through its anastomosis with the pneumogas- 

 tric. According to Cruveilhier. it sometimes comes directly and exclu- 

 sively from the anastomotic branch of the spinal accessory; sometimes 

 partly from this and partly from the pneumogastric itself. The results 

 obtained by experiment also indicate a double source for the motor 

 fibres which join the glossopharyngeal before its exit from the skull. 

 If these fibres were derived exclusively from the facial or exclusively 

 from the spinal accessory, the division or destruction of one or the 

 other of these nerves above its communicating branch would abolish 

 entirely the motor power of the glossopharyngeal. But the experiments 

 of Bernard upon rabbits, in which the facial nerve was divided in the 

 aqueduct of Fallopius, and those of Bernard and Longet on cats and 

 rabbits, in which the spinal accessory was destroyed on both sides, 

 show that the process of deglutition, though more or less retarded, is 

 not abolished by either of these ope rations. 



