HYPOGLOSSAL NERVE. 323 



movements, through the medium of the spinal nerves. Both Valentin and Dr. Reid, however, 

 positively deny that this is the case. Dr. Reid's method of experimenting was well adapted 

 to test the truth of the assertion. Considering that, in the ordinary condition of the animal, 

 it might be difficult to distinguish the actions of particular muscles, beneath the skin, when 

 those in the neighbourhood were in operation ; and also that the usual automatic movements 

 might be simulated by voluntary action, when the breathing might be rendered difficult; he 

 adopted the following plan : A small dose of prussic acid was given to an animal, in which 

 the Spinal Accessory had been previously divided on one side ; and after the convulsive 

 movements produced by it had ceased, the animal was generally found in a state similar to 

 mat which we sometimes see in apoplexy, the action of the heart going on, the respirations 

 being slow and heaving, and the sensorial functions appearing to be completely suspended. 

 The Respiratory movements always ceased before the action of the heart; but they con- 

 tinued, in several of the animals experimented on, sufficiently long to allow the muscles of 

 the anterior part of the neck to be laid bare, so that accurate observations could be made 

 upon their contractions. In the clog and cat, the sterno-mastoid does not appear to have 

 much participation in the ordinary movements of respiration ; for in several instances it 

 could not be seen to contract on either side, though the head was forcibly pulled towards the 

 chest at each inspiratory movement, chiefly by the action of the sterno-hyoid and thyroid 

 muscles. In two dogs and one cat, however, in which the head was fixed, and these 

 respiratory movements were particularly vigorous, distinct contractions were seen in the 

 exposed sterno-mastoid muscles, synchronous with the other movements of respiration : these 

 were, perhaps, somewhat weaker on the side on which the nerve had been cut, but were 

 still decidedly present. In one of these dogs, similar movements were observed in the 

 trapezius, on the side on which the nerve had been divided. As the condition of the animal 

 forbade the idea that volition could be the cause of these movements, it can scarcely be ques- 

 tioned that Sir C. Bell's statement was an erroneous one. As far, therefore, as these experi- 

 ments afford any positive data, in regard to the functions of this nerve, it may be concluded 

 that they are the same as those of the cervical plexus, with which it anastomoses freely. 

 "Future anatomical researches," as Dr. Reid justly remarks, "may perhaps explain to us how 

 it follows this peculiar course, without obliging us to suppose that it has a reference to any 

 special function in the adult of the human species." Thus, the study of the history of 

 development has accounted satisfactorily for the peculiar course of the recurrent laryngeal, 

 which may be traced passing directly from the par vagum to the larynx, at a time when the 

 neck can scarcely be said to exist, and when that organ is buried in the thorax. As this 

 rises in the neck, the nerve, which at first came off below the great transverse blood-vessels, 

 has both its origin and its termination carried upwards ; whilst it is still tied down by these 

 vessels in the middle of its course. 



418. The Hypoglossal nerve, or Motor Linguse, is the only one which, 

 in the regular order, now remains to be considered. 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 spoke of it as the nerve of the motions of 

 articulation, 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 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 pro- 

 perties, 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 hypoglossal 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 ; 



