FUNCTIONS OF THE CEPHALIC NERVES. 171 



alluded to in part ; but there still remain several questions to be discussed in 

 regard to them. Reasons have been given for the belief, that it is chiefly an 

 afferent nerve, scarcely having any direct power of exciting muscular con- 

 traction, but conveying impressions to the Medulla Oblongata, which produce 

 reflex movements of the other nerves ( 192). Some experimenters assert, 

 that they have succeeded in exciting direct muscular actions through its trunk. 

 This is by no means impossible ; but if the truth of the statement be admitted, 

 it does not invalidate the inferences regarding the general function of the 

 nerve, deduced by Dr. Reid from minute anatomical investigation, and from a 

 large number of experiments. Much controversy has taken place on the 

 question, whether this nerve is to be regarded as ministering, partly or exclu- 

 sively, to the sense of Taste; and many high authorities have ranged them- 

 selves on each side. The question involves that of the function of the Lingual 

 branch of the Fifth pair ; and it is partly to be decided by the anatomical rela- 

 tions of the two nerves respectively. The glosso-pharyngeal is principally 

 distributed on the mucous surface of the fauces, and on the back of the tongue. 

 According to Valentin, it sends a branch forwards, on either side, somewhat 

 beneath the lateral margin, which supplies the edges and inferior surface of 

 the tip of the tongue, and inosculates with the Lingual branch of the Fifth 

 pair. On the other hand, the upper surface of the front of the tongue is sup- 

 plied by this lingual branch. The experiments of Dr. Alcock, whose conclu- 

 sions are borne out by Dr. J. Reid, decidedly support the conclusion, that the 

 gustative sensibility of this part of the tongue is due to the latter nerve, being 

 evidently impaired by division of it. Moreover, cases are by no means rare, 

 in which the gustative sensibility of the anterior part of the tongue has been 

 destroyed, with its tactual sensibility ; when there was no reason to suppose 

 that any other than the Fifth pair of nerves was involved.* On the other 

 hand, it is equally certain, that the sense of taste is not destroyed by section of 

 the Lingual nerve on each side ; and it seems also well ascertained, that it is 

 impaired by section of the Glosso-pharyngeal nerve. Considering how nearly 

 allied is the sense of taste to that of touch, and bearing in mind the respective 

 distribution of these two nerves, it does not seem difficult to arrive at the con- 

 clusion, that both nerves are concerned in this function ; but there seems good 

 reason to believe the Glosso-pharyngeal to be exclusively that through which 

 the impressions made by disagreeable substances taken into the mouth are 

 propagated to the Medulla Oblongata, so as to produce nausea and to excite 

 efforts to vomit. 



229. The functions of the Par Vagum at its roots have lately been made 

 the subject of particular examination by Valentin; and he has arrived at the 

 very interesting result, that it there possesses no motor power, but is entirely 

 a sensory or rather an afferent nerve. He states that, if the roots be carefully 

 separated from those of the Glosso-Pharyngeal, and (which is a matter of some 

 difficulty) from those of the Spinal Accessory nerve, and be then irritated, no 

 movements of the organs supplied by it can be observed. On the other hand, 

 if the roots be irritated whilst in connection with the nervous centres, muscular 

 contractions, evidently of a reflex character, result from the irritation ; and 

 strong evidences of their sensibility are also given. On the other hand, again, 

 when the roots of the Spinal Accessory nerve are irritated, no indications of 

 sensation 'are given ; but the muscular parts supplied by the Par Vagum, as 

 well as by its own trunk, are made to contract, even when the roots are sepa- 

 rated from the nervous centres ; so that these roots must be regarded as the 

 channel of the motor influence, transmitted to them from the Medulla Oblon- 

 gata. When the Par Vagum swells into the jugular ganglion, an interchange 



* Romberg, in Mailer's Archiv. 1838, Heft iii. 



