MOTOR NERVES FUNCTIONS OF THE SENSORY GANGLIA. 655 



attempted by Flourens to show, that the division of the Auditory nerve which 

 proceeds to the Semicircular canals, has functions altogether different from 

 that portion which supplies the Vestibule and Cochlea. This inference, 

 however, is grounded only upon the movements exhibited by animals in 

 which these nerves are irritated; which movements are capable of a different 

 explanation ( 526). 



520. The nerves which minister to the sense of Taste are destitute of the 

 peculiarities which distinguish the preceding ; being no other than certain 

 branches of ordinary afferent nerves the Fifth Pair and Glosso-pharyngeal 

 ( 490-493) the peculiar endowments of which seem to depend rather upon 

 the structure and actions of the papillae at their peripheral extremities, than 

 upon anything special in their own character ; for, as in the case of the ordi- 

 nary nerves of " common" sensation, mechanical irritation applied to them 

 calls forth indications of pain. From the observations and experiments of 

 M. Cl. Bernard, 1 it appears that the facial nerve (portio dura of the 7th) 

 supplies some condition requisite for the sense of Taste, through the branch 

 known as the Chorda Tympani, which is the motor nerve of the Lingualis 

 muscle and Submaxillary gland ( 105). When paralysis of the Facial 

 exists in Man, the sense of taste is very much impaired on the correspond- 

 ing side of the tongue, provided that the cause of the paralysis be seated 

 above the origin of the Chorda Tympani from its trunk. Similar results 

 have been obtained from experiments upon other animals. The effect may 

 possibly be attributable to the secretion of Saliva being interfered with. 



521. Nerves of Common Sensation. To the sense of Touch all the afferent 

 nerves of the body (save the nerves of special sense) appear to minister ; in 

 virtue according to the doctrine already propounded (485) of the direct 

 connection of certain of their fibrils with the Sensorium commune. But the 

 degree in which they are capable of producing Sensations does not bear any 

 constant relation to their power of exciting reflex actions. Thus, the Glosso- 

 pharyngeal is not nearly so sensitive as the Fifth pair ; though more power- 

 ful as an excitor nerve. The Par Vagum appears to have even less power 

 of arousing sensory changes ; although it is the most important of all the 

 excitors to reflex action. So again, the afferent nerves of the inferior ex- 

 tremities, in Man, are less concerned in ministering to sensations, than are 

 those of the superior ; and yet they appear to be much more efficient as ex- 

 citors to muscular movement. These differences may be accounted for, by 

 supposing that the proportion which the fibres having their centre in the 

 ganglionic matter of the Spinal Cord, bears to that of the fibres which pass 

 on to the Sensorium, is not constant, but is liable to variation in different 

 nerves ; the former predominating in the Par Vagum and the Glosso-pharyn- 

 geal, whilst the latter are more numerous in the Fifth pair, and in most of 

 the Spinal nerves. 



522. Motor Nerves. N"o motor nerves issue from the Sensory Ganglia 

 with the same directness that afferent nerves proceed towards them ; but 

 the reflex actions of these centres find a ready channel in the motor nerves 

 of the Cranio-spinal axis generally. For, as we have seen ( 513), the 

 motor tract of the Crura Cerebri, which is in connection with the motor 

 Encephalic nerves, and also (through the vesicular substance of the Spinal 

 Cord) with the anterior roots of the Spinal nerves, passes up into the Cor- 

 pora Striata and Corpora Quadrigemiua. Although the direct connection 

 of the other ganglia of Special Sense with the Motor columns is at present 

 a matter of presumption only, yet this presumption is strongly supported 

 by the analogy of the Optic ganglia ; the distinctness of this connection 



1 Archives Generales de Medecine, 1844. 



