THE CRANIAL NERVES. 603 



both phonation and respiration and not infrequently causing death. The 

 fibers of the inferior laryngeal nerve are derived from the eleventh nerve, 

 the spinal accessory. 



The Cardiac Nerves. Faradization of the trunk of the vagus or of the 

 peripheral end of the divided nerve gives rise to a diminution in the frequency 

 and force of the heart's contractions; and if the stimulation be sufficiently 

 powerful, completely arrests it in the phase of diastole. To these results the 

 term inhibition is applied. Division of the vagi or of the cardiac branches 

 is followed by an increase in the number of contractions from loss of inhibitor 

 influences. The inhibitor fibers of the vagus are generally believed to be 

 derived from the spinal accessory, though this has been questioned. Accord- 

 ing to the recent investigations of Schaternikoff and Friedenthal, they come 

 direct in the vagus, from a nucleus near the vagal motor nucleus in the med- 

 ulla, the spinal accessory sending no branches to the heart. In the frog 

 and other batrachia the vagus contains also accelerator or augmentor fibers 

 derived from the sympathetic; hence stimulation, especially if feeble, may 

 increase the heart's action. 



The Pulmonic Nerves. The pulmonic nerves, given off from the trunk 

 after its entrance into the thorax, do not lend themselves readily to ex- 

 perimentation. Division of both vagi in the neck above the point of exit 

 of the pulmonic branches is followed by a decrease in the frequency of the 

 respiratory acts, with an increase in their depth. At the same time there is 

 a loss of sensibility of the mucous membrane of the trachea and lungs and 

 a paralysis of non-striated muscle-fibers. 



Stimulation of the central end of the divided vagus with weak induced 

 electric currents, increases the frequency, but decreases the amplitude, of the 

 respiratory movements. This would indicate that in the physiologic state 

 these nerve-fibers conduct afferent nerve impulses that inhibit the inspiratory 

 discharge and lead to an expiratory movement sooner than would otherwise 

 be the case. If the stimulation be increased in intensity the inspiratory 

 movement gradually so exceeds the expiratory that the inspiratory muscles 

 pass into the condition of tetanus and the chest walls come to rest in the 

 condition of forced inspiration. 



Feeble stimulation of the vagus not infrequently inhibits the inspiratory 

 movement and increases the expiratory until there is a complete cessation 

 of movement in the condition of expiratory standstill. The effect thus pro- 

 duced is similar to, if not identical with, that produced by stimulation of the 

 superior laryngeal nerve. (See page 418.) 



Faradization of the trunks of the pulmonic branches or stimulation of 

 their peripheral terminations in the mucous membrane of the bronchial 

 tubes or alveoli by the inhalation of chemic vapors causes arrest of respira- 

 tory movements, a fall of blood-pressure, and a reflex inhibition of the heart 

 (Brodie). 



Gastric Nerves. Stimulation of the peripheral end of a divided vagus 

 nerve causes a distinct contraction of the right half of the stomach and 

 secretion from the gastric glands. Division of the nerve abolishes the sen- 

 sibility of the mucous membrane of the stomach, impairs motility, and inter- 

 feres with the secretion of the gastric juice. 



Similar experimentation on the trunk of the vagus has shown that the 



