The finer Anatomy of the Nervous System of Myxine glutinosa. 395 



rest of the fibres turn in a caudal direction and are lost amongst 

 the gray matter situated along the brain surface (Fig. 17). This 

 sensory nerve is in its central origin exactly like the previous cranial 

 nerve and centrifugally it follows the motor Vagus nerves in their 

 caudal course, running above the same, as may be seen in Fig. 22. 



Like Sanders, I have always found the motor root of the Vagus 

 to consist of three nerve bundles. FtJRBRiNGER's statement that it 

 should vary from one to four bundles may perhaps be explained 

 through loss of one or more bundles in the preparation. The oc- 

 casions on which he found four roots must have been when both 

 the Lateral nerve and the Vagus bundles remained. 



The fibres spring from a ganglion consisting of mostly tripolar 

 cells, situated near the surface of the brain (Fig. 18). Not having 

 been able to obtain any satisfactory Golgi preparations of this 

 region, I am unable to give any farther details of the origin of this 

 nerve. 



The Twelfth Nerve, or the Nervus Hypoglossus. 



Below the Vagus, at the place where the spinal cord widens 

 into the Medulla oblongata, a nerve is found which, by some authors, 

 is considered a spinal nerve, by Fürbringer (12) is called a spino- 

 occipital nerve and the character of which Sanders (41) considers 

 uncertain. He says that »It is just possible that this may correspond 

 to the root in Petromyzon which Schlemm and D'Alton (42) con- 

 sidered to be the hypoglossal; but I think it more probable that in 

 this case it is part of the Vagus, but the question is rather 

 obscure, the nerve being so minute and its further course not being 

 visible«. 



As the origin of this nerve differs from the spinal nerves, I 

 consider that it must be reckoned as a cranial nerve. 



After entering the cord the sensory spinal nerves run straight 

 to the central gray, where the fibres end free amongst the cells or 

 where they bifurcate, or spring from the small cells (Fig. 17 N.Sp.P). 

 The nerve which I homologise with the Hypoglossal has, however, 

 also an independent end nucleus. Part of the fibres seem to enter 

 the central gray but the majority enter an independent nucleus of 

 gray matter situated half way between the surface of the cord and 

 the central gray. The corresponding motor nerve hardly differs 

 from the spinal one. We have here a nerve which represents a 

 medium between the Spinal sensory nerves and the cranial ditto. 



Morpholog. Jahrbttcb. "J'J. 27 



