624 FUNCTIONS OP THE CEREBRO -SPIN A L NERVOUS SYSTEM. 



still perform the voluntary movements, through the medium of the spinal 

 nerves. Both Valentin and Dr. J. Reid, however, positively deny that this 

 is the case; and Dr. Reid's method of experimenting was well adapted to 

 test the truth of the assertion. 1 The functions of this nerve have been made 

 the subject of special examination by M. Cl. Bernard ; 2 who has arrived at 

 the conclusion that the Spinal Accessory is essentially a motor nerve, whose 

 action is not exclusively requisite for the ordinary movements of respiration, 

 these being provided for by the Pneumogastric and ordinary Spinal nerves ; 

 but that its special function is to bring the respiratory movements into ac- 

 cordance with the requirements of Animal life, adapting the actions of the 

 muscles of the larynx and thorax to the production of voice, or to general 

 muscular effort. The internal branch, which is specially distributed, with 

 the fibres of the Pneumogastric, to the pharynx and larynx, is peculiarly 

 subservient to the former of these purposes; and the external to the latter. 

 This conclusion is sufficiently in accordance with the results obtained by 

 other experimenters, to be received as a probable explanation of the facts 

 which have been observed by them. 



497. The Hypoglossal nerve, or Motor Line/we, is the only one which, in 

 the regular order, now remains to be considered. This nerve contains from 

 4500 to 5000 nerve-fibres. That the distribution of this nerve is restricted 

 to the muscles of the tongue, is a point very easily established by anatomical 

 research ; and accordingly we find that, long before the time of Sir C. Bell, 

 Willis had spoken of it as the nerve of the motions of articulation, whilst 

 to the Lingual branch of the 5th 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 upon 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 among 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 hypoglossal nerve has been found to possess a small posterior root with 

 a ganglion ; this is the case in the Ox and Cat, 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 originate 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 



1 Sco his Physio!., Puthol., and Anat. Researches, p. 151; and Edin. Med. and 

 Surg. Journ., Jim. 1838. 



2 Recherches Kxporimentales sur les Functions du Nerf Spinal, in Archives de 

 Mdecine, 1S44. See ulso M. Bernard's Lecons sur la Phys. du Systeme Nervrnx, 

 torn ii, p. '279 et seq., 1858; M. Vulpian, Rev. des Cours Scient., torn, iii, p. 754; 

 mid Heidenhain, Slud. des Phy.-iolog. Inst. zu Bre.slau, 1865, p. 115. Heidenhain 

 and JSdiitt think the Spinal Accessory ministers to both the ordinary respiratory and 

 to the phonetic movements of the larynx. 



