PHYSIOLOGY OF THE CRANIAL NEKVES. 54:3 



3. The superior laryngeal nerve is chiefly sensory: the muscles supplied 

 by it being the crico-thyroid, the arytenoid in part (?), and the inferior 

 constrictor of the pharynx. 4. The motions of the oesophagus, the 

 stomach and part of the small intestines are dependent on motor fibres 

 of the vagus, and are probably excited by impressions made upon sensi- 

 tive fibres of the same. 5. The cardiac branches communicate, from 

 the centre in the medullary channel, impulses (inhibitory) regulating 

 the action of the heart. 6. The pulmonary branches form the principal 

 channel by which the sensory impressions on the mucous surface of the 

 trachea, bronchi and lungs that influence respiration, are transmitted to 

 the medulla oblongata; and some fibres also supply motor influence to 

 the muscular portions of the fibres of the trachea and bronchi. 7. 

 Branches to the stomach and intestine not only convey motor but also 

 vaso-motor impulses to those organs. 8. The action of the so-called de- 

 pressor branch (p. 149) in inhibiting the action of the vaso-motor centre 

 has already been treated of, and also the influence of the vagus in stimu- 

 lating the secretion of the salivary glands, as in the nausea which pre- 

 cedes vomiting. 



To summarize, therefore, the many functions of this nerve, it may be 

 said that it supplies (1) motor influence to the pharynx and oesophagus, 

 stomach and small intestine, the larynx, trachea, bronchi and lung; (2) 

 sensory and in part (3) vaso-motor influence in the same regions; (4) 

 inhibitory influence to the heart ; (5) inhibitory afferent impulses 

 to the vaso-motor centre ; (6) excito-secretory to the salivary 

 glands; (7) excito-motor in coughing, vomiting, etc. 



Effects of Section. Division of both vagi, or of both their recurrent 

 branches, is often very quickly fatal in young animals; but in old ani- 

 mals the division of the recurrent nerve is not generally fatal, and that 

 of both vagi is not always fatal, and, when it is so, death ensues slowly. 

 This difference is, probably, because, the yielding of the cartilages of the 

 larynx in young animals permits the glottis to be closed by the atmo- 

 spheric pressure in inspiration, and they are thus quickly suffocated 

 unless tracheotomy be performed. In old animals, the rigidity and 

 prominence of the arytenoid cartilages prevent the glottis from being 

 completely closed by the atmospheric pressure; even when all the mus- 

 cles are paralyzed, a portion at its posterior part remains open, and 

 through this the animal continues to breathe. 



In the case of slower death, after division of both the vagi, the lungs 

 are commonly found gorged with blood, oedematous, or nearly solid, with 

 a kind of low pneumonia, and with their bronchial tubes full of frothy 

 bloody fluid and mucus, changes to which, in general, the death may be 

 proximately ascribed. These changes are due, perhaps in part, to the 

 influence which the nerves exercise on the movements of the air-cells and 

 bronchi; yet, since they are not always produced in one lung when its 



