FUNCTIONS OF THE CEPHALIC NERVES. 179 



muscular movements are observed on irritating the nerve in the recently killed 

 animal, as during life. 



240. According to SirC. Bell, the Spinal Accessory is a purely Respiratory 

 nerve, whose office it is to excite the involuntary or automatic movements of 

 the muscles it supplies, which share in the act of respiration ; and he states 

 that the division of it paralyzes the muscles to which it is distributed, as 

 muscles of respiration ; though they still perform the voluntary movements, 

 through the medium of the spinal nerves. Both Valentin and Dr. Reid, how- 

 ever, positively deny that this is the case. Dr. Reid's method of experiment- 

 ing 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 neighbour- 

 hood were in operation ; and also that the usual automatic movements might 

 be stimulated 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 that 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 continued, 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 dog 

 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, syn- 

 chronous 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 ob- 

 served 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 questioned that Sir C. Bell's statement 

 was an erroneous one. As far, therefore, as these experiments 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 anasto- 

 moses 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 termina- 

 tion carried upwards ; whilst it is still tied down by these vessels in the middle 

 of its course. 



241. The Hypoglossal nerve, or Motor Liriguse, 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 



