THE CRANIAL NERVES. 555 



The Pharyngeal Nerves. Faradization of the pharyngeal nerves 

 consisting of both afferent and efferent fibers, gives rise to sensations 

 of pain, contraction of the pharyngeal muscles; and perhaps to vomit- 

 ing. Division of these nerves is followed by a loss of sensibility in 

 the parts to which they are distributed and by paralysis of the muscles 

 with a consequent impairment of deglutition. 



The Superior Laryngeal Nerve. Faradization of the superior 

 laryngeal nerve gives rise to sensations of pain, and to contraction of 

 the crico-thyroid muscle. Through reflected impulses it causes con- 

 traction of the muscles of deglutition, and of the muscles concerned 

 in the act of coughing; inhibition of the inspiratory movement and 

 arrest of respiration in the condition of expiratory standstill, with 

 perhaps a tetanic contraction of the expiratory muscles; and con- 

 traction of the laryngeal muscles with closure of the glottis. Periph- 

 eral stimulation of this nerve e. g., the contact of foreign particles 

 gives rise to a similar series of phenomena. Division of these nerves 

 is followed by a loss of sensibility in the laryngeal mucous membrane, 

 paralysis of the crico-thyroid muscle with a consequent lowering of 

 the pitch, and a diminution in the clearness of the voice. In conse- 

 quence of the loss of the sensibility there is an inability to perceive 

 the entrance of foreign bodies into the larynx. 



The Depressor Nerve. Stimulation of the peripheral end of the 

 depressor nerve is without effect; stimulation of the central end re- 

 tards and even arrests the heart's pulsations and lowers the general 

 blood-pressure. These two effects, though associated, are neverthe- 

 less independent of each other. If the vagus nerves be divided on 

 both sides between the origin of the depressor and the origin of the 

 cardiac nerves, and the former stimulated, there will be a fall of 

 pressure without retardation of the heart. The effect on the heart 

 is attributed to a stimulation of the cardio-inhibitory mechanism in 

 the medulla oblongata. 



The fall of general blood-pressure was formerly attributed to a 

 sudden dilatation of the splanchnic blood-vessels alone, in conse- 

 quence of a depression of that portion of the general vaso-motor center 

 which maintains through the splanchnic nerves a tonic contraction of 

 their walls. It has been satisfactorily demonstrated that this is not 

 the sole cause ; for after division of the splanchnic nerves, stimulation 

 of the depressor causes a still further fall of from 30 to 40 per cent, 

 in the general pressure (Porter and Beyer). Evidently, not any one, 

 but all portions of the vaso-motor center are subject to the effects of 

 depressor stimulation. 



The Inferior Laryngeal Nerves. Faradization of the inferior 

 laryngeal nerves produces effects which vary in accordance with the 

 strength of the stimulus, with different animals, and with the same 

 animal at different periods of life. In the adult dog and in man, the 



