THE PXEUMOGASTRIC NERVE. 563 



lungs, the diminished aperture of the glottis, and the 

 loss of the due nervous influence upon the process of 

 respiration. 



4. Respecting the influence of the pneumogastric nerves 

 on the movements of the oesophagus and stomach, the 

 secretion of gastric fluid, the sensation of hunger, absorp- 

 tion by the stomach, and the action of the heart,* former 

 pages may be referred to. 



Cyon and Ludwig have discovered that a remarkable 

 power appears to be exercised on the dilatation of the 

 blood-vessels by a small nerve which arises, in the rabbit, 

 from the superior laryngeal branch, or from this and 

 the trunk of the pneumogastric nerve, and after com- 

 municating with filaments of the inferior cervical ganglion 

 proceeds to the heart. If this nerve be divided, and its 

 upper extremity be stimulated by a weak interrupted cur- 

 rent, an inhibitory influence is conveyed to the vaso-motor 

 centre in the medulla oblongata (p. 576), so as to cause, 

 by reflex action, dilatation of the principal blood-vessels, 

 with diminution of the force and frequency of the heart's 

 action. From the remarkable lowering of the blood- 

 pressure in the vessels, thus produced, this branch of the 

 vagus is called the depressor nerve ; and it is presumed, 

 as an afferent nerve of the heart, to be the means of 

 conveying to the vaso-motor centre in the medulla indica- 

 tions of such conditions of the heart as require a lowering 

 of the blood pressure in the vessels; as, for example, 

 when the heart cannot, with sufficient ease, propel blood 

 into the already too full or too tense arteries. 



* See foot-note, p. 577. 



o o 2 



