344 FUNCTIONS OF THE NERVOUS SYSTEM. 



depend rather upon the structure and actions of the papillae at their peripheral 

 extremities, than upon anything special in their own characters. From the 

 recent observations and experiments of M. Ch. Bernard, 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. When paralysis of the Facial 

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

 side of the tongue, provided the cause of the paralysis be seated above the 

 origin of the Chorda Tympani from its trunk. Similar results have been ob- 

 tained from experiments upon other animals. The nature of the influence 

 afforded by this nerve is entirely unknown ; and it is the more obscure, as the 

 Chorda Tympani contains no sensory filament. 



448. 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 hypo- 

 thesis here upheld 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 powerful as an excitor nerve. The Par Vagura 

 appears to have even less power of arousing sensory changes ; although it is 

 the most important of all the exciters to reflex action. So again, the afferent 

 nerves of the inferior extremities, 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 excitors to muscular action. These differences may be ac- 

 counted for, by supposing that the proportion which the fibres, having their 

 centre in the ganglionic matter of the Spinal Cord, bear to that of the fibres 

 which pass on to the Sensorium, is not constant, but is liable to variation ; 

 the former predominating in the Par Vagum and the Glosso-pharyngeal ; 

 whilst the latter are more numerous in the Fifth Pair, and in most of the Spi- 

 nal nerves. 



449. It appears, from what has been already stated, that all the motor fibres 

 of the Cerebro-spinal system, not exclusively concerned in Reflex movements, 

 must be in connection with the Sensory ganglia ; since we find that their 

 actions, whether simply consensual, emotional, or volitional, are dependent 

 upon guiding sensations. Of these sensations, the greater proportion are 

 received from the muscles themselves ; but there are certain cases, as we have 

 seen, in which the guiding influence is communicated rather by the organs 

 and nerves of Special sense. Of these, a good example is afforded by the 

 movements of the Eyeball, presently to be examined in detail ; and another 

 is to be found in those of the Larynx, to be fully treated of hereafter (Chap, 

 viii.). The Emotions, in like manner, may operate upon all the motor nerves 

 of the body; as we see in the violent movements of unrestrained passion, or 

 in the increased power given to voluntary efforts, by the simultaneous excite- 

 ment of certain emotional states. But, as already remarked, their ordinary 

 action is most displayed through the motor nerves of the face and respiratory 

 organs. 



450. Consensual Movements of the Eye. It will be recollected that, in 

 the Human Orbit, six muscles for the movements of the eyeball are found, 

 the four recti, and the two oblique muscles. The precise actions of these are 

 not easily established by experiment on the lower animals; for in all those 

 which ordinarily maintain the horizontal position, there is an additional mus- 

 cle, termed the retractor, which embraces the whole posterior portion of the 

 globe, and passes backwards to be attached to the bottom of the orbit. This 

 muscle is most developed in Ruminating animals, which, during their whole 

 lime of feeding, carry their heads in a dependent position. In most Carni- 



