THE CENTRAL NERVOUS SYSTEM 725 



tion for the larynx above the vocal cords, and the motor nerve 

 of the crico-thyroid muscle. The inferior or recurrent 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, stimulation of which 

 gives rise to coughing, slows respiration, or stops it in expiration. 

 Reflex movements of deglutition are also caused. The vagus sup- 

 plies the lung both with motor and sensory filaments through the 

 pulmonary plexus. The motor fibres when stimulated cause con- 

 striction 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 /A 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 glosso-labio- 

 laryngeal palsy a condition characterized by progressive paralysis 

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

 the orbicularis oris is paralyzed, while the other muscles supplied 

 by the facial remain intact, would seem to show 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, may be supposed to take on a 

 similar bias or tendency to degeneration, a tendency not indicated, it 

 may be, by any structural peculiarity, but traced deep in the molecular 

 activity of the cells. Difficulty in swallowing is the chief symptom 

 of pharyngeal paralysis. The symptoms of laryngeal paralysis have 

 been already described under 'Voice' (p. 270). 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 



