vii THE MEDULLA OBLONGATA 397 



on the laryngeal muscles and heart, what muscles do they inner- 

 vate? The effects of intracranial excitation of the roots of the 

 accessory must be investigated in order to solve this problem. 

 The results obtained by Bentz and Longet from their experiments 

 on dogs suggest that the chief part of the pharyngeal muscles are 

 innervated by the accessory ; Chauveau, on the contrary, experi- 

 menting with horses, only obtained a contraction from the upper 

 part of the first pharyngeal constrictor. More interesting, because 

 probably applicable to man, are the later experiments of Beevor 

 and Horsley (1888) upon monkeys ; they obtained contraction of 

 the levator palati, azygos uvulae, and a large part of the muscula- 

 ture of the pharynx, by stimulating the roots of the accessory after 

 rapid extirpation of one cerebral and cerebellar hemisphere. 



IV. We have already, in previous chapters of this book, referred 

 to the various and important functions of the Vagus or 10th nerve 

 (formerly misnamed " pneumogastric "). Now, therefore, we need 

 only summarise them, and add such experimental facts as we have 

 not had the opportunity of discussing elsewhere. 



The branches of the vagus are of course distributed to the 

 head, neck, thorax, and abdomen, i.e. to many different visceral 

 and somatic organs (Fig. 212). 



Cl. Bernard and others demonstrated the existence of sensory 

 roots, but after giving off the superior laryngeal, the proportion of 

 sensory fibres in the vagus trunk is small, especially in rabbits. 

 The inferior laryngeal consists for the most part of motor fibres. 



The branches of the vagus contain fibres with various 

 functions : 



(a) The sensibility of the posterior part of the meninges is due 

 to the meningeal branch, which leaves the jugular ganglion and 

 accompanies the posterior branch of the meningeal artery. It is 

 probable that the vomiting in meningitis is reflexly produced by 

 the excitation of this branch of the vagus. 



(&) The sensibility of the pinna and external auditory meatus 

 is partly supplied by the auricular branch, which also comes from 

 the jugular ganglion. 



Irritation of the area innervated by the auricular nerve may 

 produce reflex vomiting and coughing, as well as reflex contraction 

 of the vessels of the ear (Snellen, Loven). 



(c) The pharyngeal branch or branches that run from the 

 ganglion nodosum to form the pharyngeal plexus contain sensory 

 fibres for the mucous membrane of the pharynx, and motor fibres 

 for the three pharyngeal constrictors. Both these come into play 

 in deglutition and vomiting. 



(d) The mucous membrane of the posterior part of the tongue, 

 epiglottis, and larynx (especially the part above the glottis) owes its 

 excessive sensibility, by which the least mechanical stimulus evokes 

 repeated fits of convulsive coughing, to the sensory fibres of the 



