826 A MANUAL OF PHYSIOLOGY 



laryngeal supplies the rest of the laryngeal muscles, and the sensory 

 fibres for the mucous membrane of the trachea and the larynx below 

 the glottis. The superior laryngeal contains afferent fibres, stimula- 

 tion of which gives rise to coughing, slows respiration, or stops it 

 in expiration. Reflex movements of deglutition are also caused. 

 The vagus supplies the lung both with motor and sensory filaments 

 through the pulmonary plexus. The motor fibres when stimulated 

 cause constriction of the bronchi ; excitation of the afferent fibres 

 causes reflex changes in the rate or depth of respiration. The 

 cardiac branches contain inhibitory fibres probably derived from 

 the spinal accessory, and depressor fibres which pass up in the vagus 

 trunk (dog), or as a separate nerve to join the vagus or its superior 

 laryngeal branch or both (rabbit). The gastric and intestinal 

 branches contain both motor and sensory nerves for the stomach 

 and intestines. The sensory are probably large medullated fibres 

 (7 /* to 9 /*). The afferent vagus fibres from the stomach carry up 

 impulses which excite the action of vomiting. Lesions of the vagus, 

 its nuclei of origin, or its branches, are associated with many 

 interesting forms of paralysis and other symptoms. Paralysis of 

 the pharynx is generally caused by disease of the nucleus in the 

 medulla. From its anatomical relation to the nuclei of the glosso- 

 pharyngeal and hypoglossal, it will be easily understood that these 

 nerves are often involved in localized central lesions along with the 

 vagus. But the fact that in progressive bulbar palsy (glosso-labio- 

 laryngeal paralysis) a condition characterized by progressive 

 paralysis and atrophy of the muscles of the tongue, lips, larynx, 

 and pharynx the orbicularis oris and other muscles of the mouth 

 and chin are paralyzed, while the rest of the muscles supplied by 

 the facial remain intact, might seem to indicate that in system 

 diseases it is not so much anatomical groups of nerve-cells which are 

 liable to simultaneous degeneration and failure, as physiological 

 groups normally associated in particular functions. Such functional 

 groups of cells, occupied with the same kinds of labour at the same 

 times and under the same conditions, might be supposed to take on 

 a similar bias or tendency to degeneration a tendency not indi- 

 cated, it may be, by any structural peculiarity, but traced deep in 

 the molecular activity of the cells. There is no foundation for the 

 view that the lips are involved in progressive bulbar palsy because 

 the fibres of the facial which supply them arise from the hypo- 

 glossal nucleus, any more than for the idea that the upper part 

 of the face escapes because its motor fibres, while reaching it 

 in the seventh nerve, really arise from the oculo-motor nucleus 

 (Bruce). Difficulty in swallowing is the chief symptom of pharyn- 

 geal paralysis. The symptoms of laryngeal paralysis have been 

 already described under 'Voice' (p. 286). Tachycardia, or a 

 permanent increase in the rate of the heart, has been stated to occur 

 in certain cases of paralysis of the vagus, caused by disease or 

 accidental interference ; and a persistent slowing of the respiration 

 has been occasionally attributed to the same cause. But it is 

 difficult to reconcile many of these cases with experimental results, 

 for in most of them the lesion only involved one vagus ; and in 

 animals section of one vagus has no permanent effect on the rate 

 of the heart or of the respiratory movements. 



Destruction of the nerve near its origin has been sometimes found 

 associated with disappearance of the food-appetites, hunger and 

 thirst, and it has been assumed that this was due to loss of afferent 



