178 FUNCTIONS OF THE NERVOUS SYSTEM. 



serious and inevitably fatal disturbances of the heart's action would soon result. 

 That this adjustment takes place otherwise than through the medium of the 

 nervous centres, ' is evident from the fact that, in a dog, in which the par 

 vagum and sympathetic had been divided in the neck on each side, violent 

 struggling, induced by alarm, raised the number of pulsations from 130 to 260 

 per minute. It is difficult to ascertain, by experiment upon the lower animals, 

 whether simple emotion, unattended with struggling or other exertion, would 

 affect the pulsation of the heart, after section of the Vagi ; but when the large 

 proportion of the Sympathetic nerves proceeding to this, organ is considered, 

 and when it is also remembered that irritation of the roots of the upper cervi- 

 cal nerves stimulates the action of the heart through these, we can scarcely 

 doubt that both may serve as the channels of this influence, especially in such 

 animals as the dog, in which the two freely inosculate in the neck. 



239. In regard to the functions of the Spinal Accessory nerve, also, there 

 has been great difference of opinion; the peculiarity of its origin and course 

 having led to the belief that some very especial purpose is answered by it. 

 We shall first examine what evidence of its character may be obtained from 

 its anatomy only. Its filaments come off from the middle column of the Spinal 

 Cord, most frequently as low down as the origins of the sixth and seventh 

 Cervical nerves. In its course upwards to the foramen magnum, it lies 

 between the posterior roots of the spinal nerves and the ligamentum denticu- 

 latum. It sometimes receives filaments from these roots, and is generally 

 connected especially with the first cervical. According to Bellingeri, however, 

 who has paid great attention to the subject, the filaments coming from the pos- 

 terior roots do not form part of the trunk of the nerve, but leave it again to 

 enter the posterior root of the first cervical. It may be doubted whether this 

 is entirely true ; as some experiments appear to show that the Spinal Acces- 

 sory is in some degree a sensory nerve, even at its roots. As the trunk passes 

 through 'the foramen lacerum, it divides into two branches ; of which the 

 internal, after giving off some filaments that assist in forming the pharyngeal 

 branch of the Par Vagum, becomes incorporated with the trunk of that nerve, 

 whilst the external proceeds outwards, and is finally distributed to the sterno- 

 cleido-mastoideus and trapezius muscles, some of its filaments inosculating 

 with those of the cervical plexus. It is interesting to remark, that the junction 

 of the anterior branch with the Par Vagum, beyond the point at which the 

 latter swells out into its superior ganglion, increases the analogy, which has 

 been sustained upon other grounds, between the compound trunk thus formed 

 and that of the spinal nerves ; the Par Vagum being regarded as the sensory 

 root, and the Spinal Accessory as the motor. According to Valentin, however, 

 there is not a mere passage of filaments from the Spinal Accessory to the Par 

 Vagum, but an absolute interchange ; the trunk of the former containing some 

 sensory fibres derived from the latter. When the roots of the Spinal Acces- 

 sory are irritated, as appears from the experiments of Valentin, no decided 

 indications of sensation can be obtained ; but all the motor actions of the Par 

 Vagum manifest themselves. When the external branch is irritated, before it 

 perforates the sterno-mastoid muscle, vigorous convulsive movements of that 

 muscle, and of the trapezius, are produced; and the animal does not give any 

 signs of pain, unless the nerve is firmly compressed between the forceps, or 

 is included in a tight ligature. Hence it may be inferred that the functions of 

 this nerve are chiefly motor, and that its sensory filaments are few in number. 

 Further, when the nerve has been cut across, or firmly tied, irritation of the 

 lower end is attended by the same convulsive movements of tlie muscles ; 

 whilst irritation of the upper end, in connection with the spinal cord, is unat- 

 tended with any muscular movement. Hence it is clear that the motions 

 occasioned by irritating it are of a direct, not of a reflex character. The same 1 



