CHAP. XX.] THE SPINAL ACCESSORY NERVE. ]29 



of origin which emerge from the. cord quite close to the posterior 

 roots of the cervical nerves. The reply to this objection is, that the 

 external branch of the nerve is nevertheless distinctly motor, and 

 that therefore the internal may be so likewise. Morganti and Ber- 

 nard affirm that the lower roots form the external branch; if so, 

 then the superior fascicles may be those which contribute to form 

 the internal branch, and, therefore, its function probably differs 

 from that of the external branch. We have already alluded to 

 the fact that a coalition is sometimes observed between the poste- 

 rior roots of the first or second cervical nerves, and the upper roots 

 of the spinal accessory. The function of the former being confess- 

 edly sensitive, it is highly probable that the latter nerves, which are 

 apt to coalesce with them, should perform a similar office. 



To determine this question by experiment is extremely difficult, 

 by reason of the small size of the internal branch and the great 

 depth at which it is situate, which render it almost impossible to 

 expose the nerve without injuring the vagus itself. Accordingly, we 

 find the recorded statements of physiologists regarding the results of 

 such experiments quite contradictory. The greatest number of ob- 

 servers, and the most recent ones, give their evidence against the 

 motor function of the internal branch, at least against the doctrine 

 of its yielding the motor fibres of the vagus nerve. Most of them, 

 however, agree in stating that a degree of hoarseness and feebleness 

 of voice always followed the section of the internal branch, as if some 

 of the motor fibres of the laryngeal nerve were derived from it. 

 From Miiller's and Dr. John Reid's experiments, by irritation of the 

 spinal accessory nerve within the cranium, no conclusive results were 

 obtained favourable to the view which assigns motor power to the 

 internal branch; on the contrary, these experiments rather tend to 

 prove that the vagus contains within itself the motor fibres sufficient 

 for the parts it supplies. These experimenters found that irritation 

 of the trunk of the vagus, before its junction with the spinal acces- 

 sory, caused contractions of the pharyngeal and laryngeal muscles, 

 as well as of the fibres of the oesophagus. 



Respecting the external branch of the spinal accessory nerve, 

 it has been already stated that experiment confirms the results 

 deducible from anatomy. We know that the trapezius and sterno- 

 mastoid muscles receive nerves from the cervical plexus as well 

 as from the spinal accessory. If the latter be cut these muscles 

 are not paralysed, although weakened, and continue to act in 

 respiratory as well as in voluntary movements, contrary to the 

 views of Sir C. Bell, who regarded the spinal accessory nerves 



VOL. II. K 



