180 FUNCTIONS OF THE NERVOUS SYSTEM. 



the time of Sir C. Bell, Willis spoke of it as the nerve of the motions of articu- 

 lation, whilst to the Lingual branch of the fifth pair he attributed the power of 

 exercising the sense of taste ; and he distinctly stated, that the reason of this 

 organ being supplied with two nerves is its double function. The inference 

 that it is chiefly, if not entirely, a motor nerve, which has been founded on its 

 anatomical distribution, is supported also by the nature of its origin, which is 

 usually from a single root, corresponding to the anterior root of the Spinal 

 nerves. Experiment shows that, when the trunk of the nerve is stretched, 

 pinched, or galvanized, violent motions of the whole tongue, even to its tip, 

 are occasioned ; and also, that similar movements take place after division of 

 the nerve, when the cut end most distant from the brain is irritated. In regard 

 to the degree in which this nerve possesses sensory properties, there is some 

 difference of opinion amongst physiologists, founded, as it would seem, on a 

 variation in this respect between different animals. Indications of pain are 

 usually given, when the trunk is irritated after its exit from the cranium ; but 

 these may proceed from its free anastomosis with the cervical nerves, which 

 not improbably impart sensory fibres to it. But in some Mammalia, the hypo- 

 glossal nerve has been found to possess a small posterior root with a ganglion : 

 this is the case in the ox, and also in the rabbit ; and in the latter animal, 

 Valentin states that the two trunks pass out from the cranium through separate 

 orifices, and that, after their exit, one may be shown to be sensory, and the 

 other to be motor. Hence this nerve, which is the lowest of those that ori- 

 ginate in the cephalic prolongation of the spinal cord generally known as the 

 medulla oblongata, approaches very closely in some animals to the regular 

 type of the spinal nerves ; and though in Man it still manifests an irregularity, 

 in having only a single root, yet this irregularity is often shared by the first 

 cervical nerve, which also has sometimes an anterior root only. 



342. The Hypoglossal nerve is distributed not merely to the tongue, but to 

 the muscles of the neck which are concerned in the movements of the larynx ; 

 and the purpose of this distribution is probably to associate them in those 

 actions which are necessary for articulate speech. Though all the motions 

 of the tongue are performed through the medium of this nerve, yet it would 

 appear, from pathological phenomena, to have at least two distinct connections 

 with the nervous centres ; for in many cases of paralysis, the masticatory 

 movements of the tongue are but little affected, when the power of articula- 

 tion is much injured or totally destroyed ; and the converse may be occa- 

 sionally noticed. When this nerve is paralyzed on one side, in hemiplegia, 

 it will be generally observed that the tongue, when the patient is directed to 

 put it out, is projected towards the palsied side of the face : that is due to the 

 want of action of the lingual muscles of that side, which do not aid in pushing 

 forward the tip; the point is consequently directed only by the muscles of the 

 other side, which will not act in a straight direction, when unantagonized by 

 their fellows. It is a curious fact, however, that the hypoglossal nerve seems 

 not to be always palsied on the same side with the facial, but sometimes on 

 the other. This has been suggested to be due to the origination of the roots 

 of this nerve from near the point at which the pyramids of the medulla 

 oblongata decussate : so that some of its fibres come off, like those of the spinal 

 nerves, without crossing ; whilst others are transmitted to the opposite side, 

 like those of the higher cerebral nerves ; and the cause of paralysis may 

 affect one or other of these sets of roots mortfparticularly. Whatever may be 

 the validity of this explanation, the circumstance is an interesting one, and 

 well worthy of attention.* 



* It may be questioned, however, whether the Hypoglossal is really paralyzed on the 

 opposite side from the facial in such cases. An instance has been communicated to the 



