564 THE NERYOUS SYSTEM. 



probable, therefore, that the internal branch, which is 

 added to the trunk of the pneumogastric just before the 

 giving off of the pharyngeal branch, is also motor; and 

 that through it the pneumogastric nerve derives part of 

 the motor fibres which it supplies to the muscles enumer- 

 ated above. And further, since the pneumogastric nerve 

 has a ganglion just above the part at which the internal 

 branch of the accessory nerve joins its trunk, a close 

 analogy may seem to exist between these two nerves and 

 the spinal nerves with their anterior and posterior roots. 

 In this view, Arnold and several later physiologists have 

 regarded the accessory nerve as constituting a motor root 

 of the vagus nerve ; and, although this view cannot now 

 be maintained, yet it is very probable that the accessory 

 nerve gives some motor filaments to the pneumogastric. 

 For, among the experiments made on this point, s many 

 have shown that when the accessory nerve is irritated 

 within the skull, convulsive movements ensue in some of 

 the muscles of the larynx ; all of which, as already stated, 

 are supplied, apparently, by branches of the pneumo- 

 gastric ; and (which is a very significant fact) Yrolik states 

 that in the chimpanzee the internal branch of the accessory 

 does not join the pneumogastric at all, but goes direct to 

 the larynx. On the whole, therefore, although in some of 

 the experiments no movements in the larynx followed 

 irritation of the accessory nerve, yet it may be concluded 

 that this nerve gives to the pneumogastric some of the 

 motor filaments which pass, with the laryngeal branches, 

 to the muscles of the larynx, especially to the crico-thyroid 

 (Bernard). 



It is not certain, whether, besides these, the accessory 

 gives to the pneumogastric any other motor filaments ; for 

 the experiments undertaken to determine whether, on 

 irritating the accessory within the skull, the muscles of the 

 pharynx, oesophagus, or other parts besides the larynx are 

 convulsed, are completely contradictory, and there appears 



